U.S. patent number 7,738,055 [Application Number 11/626,115] was granted by the patent office on 2010-06-15 for display device having stacked polarizers that differ in degrees of light absorbing bands and that are between a pair of protective layers such that no protective layer is located between the stacked polarizers.
This patent grant is currently assigned to Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Yuji Egi, Tetsuji Ishitani, Takeshi Nishi.
United States Patent |
7,738,055 |
Egi , et al. |
June 15, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Display device having stacked polarizers that differ in degrees of
light absorbing bands and that are between a pair of protective
layers such that no protective layer is located between the stacked
polarizers
Abstract
To provide a display device having a high contrast ratio by a
simple and easy method and to manufacture a high-performance
display device at low cost, in a display device having a display
element between a pair of light-transmitting substrates, layers
each including a polarizer having different wavelength distribution
of extinction coefficient from each other with respect to the
absorption axes are stacked and provided on an outer side of the
light-transmitting substrates. Further, a retardation plate may be
provided between the stacked polarizers.
Inventors: |
Egi; Yuji (Kanagawa,
JP), Ishitani; Tetsuji (Kanagawa, JP),
Nishi; Takeshi (Kanagawa, JP) |
Assignee: |
Semiconductor Energy Laboratory
Co., Ltd. (Atsugi-shi, Kanagawa-ken, JP)
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Family
ID: |
38289999 |
Appl.
No.: |
11/626,115 |
Filed: |
January 23, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070177071 A1 |
Aug 2, 2007 |
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Foreign Application Priority Data
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Jan 31, 2006 [JP] |
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2006-023853 |
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Current U.S.
Class: |
349/96 |
Current CPC
Class: |
G02F
1/133533 (20130101); G02F 1/13363 (20130101); G02F
2203/04 (20130101); G02F 1/133531 (20210101); G02F
2203/64 (20130101) |
Current International
Class: |
G02F
1/1335 (20060101) |
Field of
Search: |
;349/96-106 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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Other References
J Chen et al.; "21.2: Optimum Film Compensation Modes for TN and VA
LCDs"; SID 98 Digest--SID International Symposium Digest of
Technical Papers; pp. 315-318; 1998. cited by other .
European Search Report (European Application No. 07001333.9), 6
pages, mailed Apr. 25, 2008. cited by other .
P. Lazarev et al,: "Thin Crystal Films (TCF) for LCD Contrast
Enhancement" SID Digest '03 : SID International Symposium Digest of
Technical Papers, pp. 669-671 (2003). cited by other .
Office Action (Application No. 200710006165.X;CN9372) Dated Jul. 3,
2009. cited by other.
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Primary Examiner: Heyman; John
Attorney, Agent or Firm: Fish & Richardson P.C.
Claims
What is claimed is:
1. A display device comprising: a first light-transmitting
substrate and a second light-transmitting substrate which are
disposed to face each other; a display element sandwiched between
the first light-transmitting substrate and the second
light-transmitting substrate; and a layer including stacked
polarizers on an outer side of the first light-transmitting
substrate or the second light-transmitting substrate, wherein: the
stacked polarizers are arranged so that their absorption axes are
deviated from a parallel Nicols state, a distribution of a degree
to which a first one of the stacked polarizers absorbs light across
a band of wavelengths differs from a distribution of a degree to
which a second one of the stacked polarizers absorbs light across
the band of wavelengths, and the stacked polarizers are provided
between a pair of protective layers arranged such that no
protective layer is located between the stacked polarizers.
2. A display device according to claim 1, wherein the display
element is a liquid crystal element.
3. A display device comprising: a first light-transmitting
substrate and a second light-transmitting substrate which are
disposed to face each other; a display element sandwiched between
the first light-transmitting substrate and the second
light-transmitting substrate; and a layer including stacked
polarizers on an outer side of the first light-transmitting
substrate or the second light-transmitting substrate; and a
retardation plate provided between the layer including the stacked
polarizers and the first light-transmitting substrate or the second
light-transmitting substrate, wherein: the stacked polarizers are
arranged so that their absorption axes are deviated from a parallel
Nicols states a distribution of a degree to which a first one of
the stacked polarizers absorbs light across a band of wavelengths
differs from a distribution of a degree to which a second one of
the stacked polarizers absorbs light across the band of
wavelengths, and the stacked polarizers are provided between a pair
of protective layers arranged such that no protective layer is
located between the stacked polarizers.
4. A display device according to claim 3, wherein the display
element is a liquid crystal element.
5. A display device comprising: a first light-transmitting
substrate and a second light-transmitting substrate which are
disposed to face each other; a display element sandwiched between
the first light-transmitting substrate and the second
light-transmitting substrate; a first layer including first stacked
polarizers on an outer side of the first light-transmitting
substrate; a second layer including second stacked polarizers on an
outer side of the second light-transmitting substrate, wherein: the
first stacked polarizers are arranged so that their absorption axes
are deviated from a parallel Nicols state, the second stacked
polarizers are arranged so that their absorption axes are in a
parallel Nicols state, a distribution of a degree to which a first
one of the first stacked polarizers absorbs light across a first
band of wavelengths differs from a distribution of a degree to
which a second one of the first stacked polarizers absorbs light
across the first band of wavelengths, a distribution of a degree to
which a first one of the second stacked polarizers absorbs light
across a second band of wavelengths differs from a distribution of
a degree to which a second one of the second stacked polarizers
absorbs light across the second band of wavelengths, and the first
stacked polarizers are provided between a first pair of protective
layers arranged such that no protective layer is located between
the first stacked polarizers, and the second stacked polarizers are
provided between a second pair of protective layers.
6. A display device according to claim 5, wherein the display
element is a liquid crystal element.
7. A display device according to claim 5, wherein the display
device further comprises a light source on an outer side of the
second stacked polarizers.
8. A display device comprising: a first light-transmitting
substrate and a second light-transmitting substrate which are
disposed to face each other; a display element sandwiched between
the first light-transmitting substrate and the second
light-transmitting substrate; a first layer including first stacked
polarizers on an outer side of the first light-transmitting
substrate; a second layer including second stacked polarizers on an
outer side of the second light-transmitting substrate; a first
retardation plate between the first layer including the first
stacked polarizers and the first light-transmitting substrate; a
second retardation plate between the second layer including the
second stacked polarizers and the second light-transmitting
substrate, wherein: the first stacked polarizers are arranged so
that their absorption axes are deviated from a parallel Nicols
state, the second stacked polarizers are arranged so that their
absorption axes are in a parallel Nicols state, a distribution of a
degree to which a first one of the first stacked polarizers absorbs
light across a first band of wavelengths differs from a
distribution of a degree to which a second one of the first stacked
polarizers absorbs light across the first band of wavelengths, a
distribution of a degree to which a first one of the second stacked
polarizers absorbs light across a second band of wavelengths
differs from a distribution of a degree to which a second one of
the second stacked polarizers absorbs light across the second band
of wavelengths, and the first stacked polarizers are provided
between a first pair of protective layers arranged such that no
protective layer is located between the first stacked polarizers,
and the second stacked polarizers are provided between a second
pair of protective layers.
9. A display device according to claim 8, wherein the display
element is a liquid crystal element.
10. A display device according to claim 8, wherein the display
device further comprises a light source on an outer side of the
second stacked polarizers.
11. A display device comprising: a first light-transmitting
substrate and a second light-transmitting substrate which are
disposed to face each other; a display element sandwiched between
the first light-transmitting substrate and the second
light-transmitting substrate; a first layer including first stacked
polarizers on an outer side of the first light-transmitting
substrate; and a second layer including second stacked polarizers
on an outer side of the second light-transmitting substrate,
wherein: the first stacked polarizers are arranged so that their
absorption axes are deviated from a parallel Nicols state, the
second stacked polarizers are arranged so that their absorption
axes are in a parallel Nicols state, the first layer including the
first stacked polarizers has a first polarizer and a second
polarizer which are sequentially stacked from the first
light-transmitting substrate side, the first stacked polarizers and
the second stacked polarizers are arranged so that their absorption
axes are in a crossed Nicols state a distribution of a degree to
which a first one of the first stacked polarizers absorbs light
across a first band of wavelengths differs from a distribution of a
degree to which a second one of the first stacked polarizers
absorbs light across the first band of wavelengths, a distribution
of a degree to which a first one of the second stacked polarizers
absorbs light across a second band of wavelengths differs from a
distribution of a degree to which a second one of the second
stacked polarizers absorbs light across the second band of
wavelengths, and the first stacked polarizers are provided between
a first pair of protective layers arranged such that no protective
layer is located between the first stacked polarizers, and the
second stacked polarizers are provided between a second pair of
protective layers.
12. A display device according to claim 11, wherein the display
element is a liquid crystal element.
13. A display device according to claim 11, wherein the display
device further comprises a light source on an outer side of the
second stacked polarizers.
14. A display device comprising: a first light-transmitting
substrate and a second light-transmitting substrate which are
disposed to face each other; a display element sandwiched between
the first light-transmitting substrate and the second
light-transmitting substrate; a first layer including first stacked
polarizers on an outer side of the first light-transmitting
substrate; a second layer including second stacked polarizers on an
outer side of the second light-transmitting substrate; a first
retardation plate between the first light-transmitting substrate
and the first layer including the first stacked polarizers; a
second retardation plate between the second light-transmitting
substrate and the second layer including the second stacked
polarizers, wherein: the first stacked polarizers are arranged so
that their absorption axes are deviated from a parallel Nicols
state, the second stacked polarizers are arranged so that their
absorption axes are in a parallel Nicols state, the first layer
including the first stacked polarizers has a first polarizer and a
second polarizer which are sequentially stacked from the first
light-transmitting substrate side, the first stacked polarizers and
the second stacked polarizers are arranged so that their absorption
axes are in a crossed Nicols states a distribution of a degree to
which a first one of the first stacked polarizers absorbs light
across a first band of wavelengths differs from a distribution of a
degree to which a second one of the first stacked polarizers
absorbs light across the first band of wavelengths, a distribution
of a degree to which a first one of the second stacked polarizers
absorbs light across a second band of wavelengths differs from a
distribution of a degree to which a second one of the second
stacked polarizers absorbs light across the second band of
wavelengths, and the first stacked polarizers are provided between
a first pair of protective layers arranged such that no protective
layer is located between the first stacked polarizers, and the
second stacked polarizers are provided between a second pair of
protective layers.
15. A display device according to claim 14, wherein the display
element is a liquid crystal element.
16. A display device according to claim 14, wherein the display
device further comprises a light source on an outer side of the
second stacked polarizers.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure of a display device
having a polarizer.
2. Description of the Related Art
A so-called flat panel display, which is a display device that is
very thin and lightweight as compared to the conventional
cathode-ray tube display device, has been developed. A liquid
crystal display device having a liquid crystal element as a display
element, a light emitting device having a self-light emitting
element, an FED (field emission display) using an electron beam,
and the like compete in the market of flat panel displays.
Therefore, lower power consumption and a higher contrast ratio are
demanded to increase the added value so as to differentiate from
other products.
In general, in a liquid crystal display device, each substrate is
provided with one polarizing plate to keep a contrast ratio. When
display of darker black is performed, the contrast ratio can be
increased accordingly. Thus, higher display quality can be provided
when an image is seen in a dark room such as a home theater
room.
For example, in order to reduce display nonuniformity caused due to
shortage of polarization degree and polarization distribution of
polarizing plates and to improve a contrast ratio, a structure is
suggested in which a first polarizing plate is provided outside a
substrate on a viewing side of a liquid crystal cell, a second
polarizing plate is provided outside a substrate on a side opposite
to the viewing side, and a third polarizing plate is provided for
increasing the degree of polarization when light from an auxiliary
light source provided on the substrate side opposite to the viewing
side is polarized through the second polarizing plate and
transmitted through the liquid crystal cell (see Reference 1: PCT
International Publication No. 00/34821).
SUMMARY OF THE INVENTION
However, a yet higher contrast ratio has been demanded to be
enhanced and researches have been made for enhancement in contrast
ratio of liquid crystal display devices. Further, there is a
problem in that a polarizing plate having a higher degree of
polarization is expensive.
A method for improving a contrast ratio by using three polarizing
plates as described in Reference 1 can be realized by using an
inexpensive polarizing plate; however, it is difficult to perform
display with a higher contrast ratio by the method. Further, the
dependence of absorption properties of a polarizer on a wavelength
is not constant, that is, the polarizer has properties of hardly
absorbing light of the certain wavelength region. Accordingly, even
when a plurality of polarizers of the same type is used in
attempting to improve contrast ratio, a certain wavelength region
of light which is hardly absorbed remains. This causes slight light
leakage, and the light leakage prevents a contrast ratio from being
enhanced.
In view of the aforementioned problems, an object of the invention
is to provide a display device having a high contrast ratio by a
simple and easy method. Another object of the invention is to
manufacture a high-performance display device at low cost.
It is a feature of the present invention that at least one of
light-transmitting substrates which are provided to face each other
is provided with a layer including stacked polarizers, and the
stacked polarizers have different wavelength distributions of
extinction coefficients and are arranged so that their absorption
axes are deviated from a parallel Nicols state. Further, a wave
plate or a retardation plate may be provided between the stacked
polarizers.
A polarizer has an absorption axis, and when polarizers are
stacked, a state where the absorption axes of the polarizers are
parallel to each other is referred to as a parallel Nicols state,
while a state where the absorption axes of the polarizers are
perpendicular to each other is referred to as a crossed Nicols
state. Note that a polarizer characteristically has a transmission
axis perpendicular to the absorption axis. Therefore, a state where
the transmission axes are parallel to each other can also be
referred to as a parallel Nicols state, and a state where
transmission axes are perpendicular to each other can also be
referred to as a crossed Nicols state.
Further, a polarizer has a specific light extinction coefficient.
This is because the dependence of the absorption properties of a
polarizer on a wavelength is not constant, and the absorption
properties with respect to a certain wavelength region are lower
than that with respective to another wavelength region, that is,
the polarizer has properties of hardly absorbing light of the
certain wavelength region. In the present invention, the absorption
axes of stacked polarizers have different wavelength distributions
of extinction coefficients.
The wavelength region of light which is hardly absorbed can be
eliminated or reduced by combining and stacking polarizers having
different wavelength distributions of extinction coefficients with
respect to the absorption axes. Thus, even slight light leakage can
be prevented and contrast ratio can be further improved.
A mode of a display device the present invention includes a first
light-transmitting substrate and a second light-transmitting
substrate which are disposed to face each other; a display element
sandwiched between the first light-transmitting substrate and the
second light-transmitting substrate; and layers including stacked
polarizers on an outer side of the first light-transmitting
substrate and the second light-transmitting substrate. The stacked
polarizers have different wavelength distributions of extinction
coefficients with respect to absorption axes, and the stacked
polarizers are arranged so that their absorption axes are deviated
from a parallel Nicols state.
A mode of a display device the present invention includes a first
light-transmitting substrate and a second light-transmitting
substrate which are disposed to face each other; a display element
sandwiched between the first light-transmitting substrate and the
second light-transmitting substrate; and layers including stacked
polarizers on an outer side of the first light-transmitting
substrate and the second light-transmitting substrate; and a
retardation plate provided between the layers including the stacked
polarizers and the first light-transmitting substrate and the
second light-transmitting substrate respectively. The stacked
polarizers have different wavelength distributions of extinction
coefficients with respect to absorption axes, and the stacked
polarizers are arranged so that their absorption axes are deviated
from a parallel Nicols state.
A mode of a display device the present invention includes a first
light-transmitting substrate and a second light-transmitting
substrate which are disposed to face each other; a display element
sandwiched between the first light-transmitting substrate and the
second light-transmitting substrate; and a first layer including
first stacked polarizers on an outer side of the first
light-transmitting substrate; and a second layer including second
stacked polarizers on an outer side of the second
light-transmitting substrate. The first stacked polarizers have
different wavelength distributions of extinction coefficients with
respect to absorption axes, the second stacked polarizers have
different wavelength distributions of extinction coefficients with
respect to absorption axes, the first stacked polarizers are
arranged so that their absorption axes are deviated from a parallel
Nicols state, and the second stacked polarizers are arranged so
that their absorption axes are deviated from a parallel Nicols
state.
A mode of a display device the present invention includes a first
light-transmitting substrate and a second light-transmitting
substrate which are disposed to face each other; a display element
sandwiched between the first light-transmitting substrate and the
second light-transmitting substrate; and a first layer including
first stacked polarizers on an outer side of the first
light-transmitting substrate; a second layer including second
stacked polarizers on an outer side of the second
light-transmitting substrate; a first retardation plate between the
first layer including the first stacked polarizers and the first
light-transmitting substrate; and a second retardation plate
between the second layer including the second stacked polarizers
and the second light-transmitting substrate. The first stacked
polarizers have different wavelength distributions of extinction
coefficients with respect to absorption axes, the second stacked
polarizers have different wavelength distributions of extinction
coefficients with respect to absorption axes, the first stacked
polarizers are arranged so that their absorption axes are deviated
from a parallel Nicols state, and the second stacked polarizers are
arranged so that their absorption axes are deviated from a parallel
Nicols state.
A mode of a display device the present invention includes a first
light-transmitting substrate and a second light-transmitting
substrate which are disposed to face each other; a display element
sandwiched between the first light-transmitting substrate and the
second light-transmitting substrate; and a first layer including
first stacked polarizers on an outer side of the first
light-transmitting substrate; and a second layer including second
stacked polarizers on an outer side of the second
light-transmitting substrate. The first stacked polarizers have
different wavelength distributions of extinction coefficients with
respect to absorption axes, the second stacked polarizers have
different wavelength distributions of extinction coefficients from
each other with respect to absorption axes, the first stacked
polarizers are arranged so that their absorption axes are deviated
from a parallel Nicols state, the second stacked polarizers are
arranged so that their absorption axes are deviated from a parallel
Nicols state, the first layer including the first stacked
polarizers has a first polarizer and a second polarizer which are
sequentially stacked from the first light-transmitting substrate
side, and the first stacked polarizers and the second stacked
polarizers are arranged so that their absorption axes are in a
crossed Nicols state.
A mode of a display device the present invention includes a first
light-transmitting substrate and a second light-transmitting
substrate which are disposed to face each other; a display element
sandwiched between the first light-transmitting substrate and the
second light-transmitting substrate; and a first layer including
first stacked polarizers on an outer side of the first
light-transmitting substrate; a second layer including second
stacked polarizers on an outer side of the second
light-transmitting substrate; a first retardation plate between the
first light-transmitting substrate and the first layer including
the first stacked polarizers; and a second retardation plate
between the second light-transmitting substrate and the second
layer including the second stacked polarizers. The first stacked
polarizers have different wavelength distributions of extinction
coefficients from each other with respect to absorption axes, the
second stacked polarizers have different wavelength distributions
of extinction coefficients from each other with respect to
absorption axes, the first stacked polarizers are arranged so that
their absorption axes are deviated from a parallel Nicols state,
the second stacked polarizers are arranged so that their absorption
axes are deviated from a parallel Nicols state, the first layer
including the first stacked polarizers has a first polarizer and a
second polarizer which are sequentially stacked from the first
light-transmitting substrate side, and the first stacked polarizers
and the second stacked polarizers are arranged so that their
absorption axes are in a crossed Nicols state.
With respect to a display device of the invention, in the case
where light from a light source called a backlight is transmitted
through a layer including stacked polarizers on a side opposite to
a viewing side to a display element and extracted from a layer
including stacked polarizers on a viewing side, it is preferable
that the absorption axes of the polarizers on the side (backlight
side) opposite to the viewing side are in a parallel Nicols state,
thereby transmittance of the light from the backlight is
increased.
Further, a layer including stacked polarizers of the display device
of the invention may have a structure in which a stack of a
plurality of polarizers is provided between a pair of protective
layers or a structure in which each polarizer is sandwiched between
a pair of protective layers. Further, a structure may be used in
which an anti-reflective film, an antiglare film, or the like is
provided on the viewing side of the layer including stacked
polarizers.
With a simple structure in which a plurality of polarizers having
different wavelength distributions of extinction coefficients are
stacked and provided so that their absorption axes are deviated
from each other, light leakage can be reduced, and contrast ratio
of a display device can be increased. Further, such a high
performance display device can be manufactured at low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIGS. 2A and 2B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIGS. 3A to 3C are a cross-sectional view, a perspective view, and
a schematic diagram of a display device of the present
invention;
FIGS. 4A and 4B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIG. 5 illustrates a display device of the present invention;
FIGS. 6A and 6B each illustrate a display device of the present
invention;
FIGS. 7A and 7B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIGS. 8A and 8B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIGS. 9A to 9C are a cross-sectional view, a perspective view, and
a schematic diagram of a display device of the present
invention;
FIGS. 10A to 10C are a cross-sectional view, a perspective view,
and a schematic diagram of a display device of the present
invention;
FIGS. 11A and 11B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIGS. 12A and 12B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIGS. 13A to 13C are cross-sectional views each illustrating a
structure of a layer including a polarizer of the present
invention;
FIGS. 14A and 14B are a top view and a cross-sectional view of a
display device of the present invention;
FIG. 15 is a cross-sectional view of a display device of the
present invention;
FIGS. 16A to 16C are top views each showing a display device of the
present invention;
FIGS. 17A and 17B are top views each showing a display device of
the present invention;
FIGS. 18A and 18B are cross-sectional views each showing a display
device of the present invention;
FIGS. 19A to 19D are cross-sectional views showing an irradiation
means of a display device of the present invention;
FIG. 20 is a block diagram illustrating a basic structure of an
electronic device to which the present invention is applied;
FIGS. 21A to 21C illustrate electronic devices of the present
invention;
FIGS. 22A to 22E illustrate electronic devices of the present
invention;
FIG. 23 is a cross-sectional view of a display device of the
present invention;
FIGS. 24A to 24C are block diagrams illustrating a display device
of the present invention;
FIGS. 25A to 25D are top views each illustrating a display device
of the present invention;
FIG. 26A to 26D are top views each illustrating a display device of
the present invention;
FIGS. 27A1 to 27C2 are cross-sectional views illustrating a liquid
crystal mode of the present invention;
FIGS. 28A1 to 28B2 are cross-sectional views illustrating a liquid
crystal mode of the present invention;
FIGS. 29A1 to 29B2 are cross-sectional views illustrating a liquid
crystal mode of the present invention;
FIGS. 30A and 30B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIGS. 31A and 31B are a cross-sectional view and a perspective view
respectively of a display device of the present invention;
FIG. 32 is a diagram showing experimental conditions of Embodiment
1;
FIG. 33 is a graph showing an experimental result of Embodiment
1;
FIGS. 34A to 34C are diagrams showing experimental conditions of
Embodiment 1;
FIG. 35 is a graph showing an experimental result of Embodiment
1;
FIG. 36 is a graph showing an experimental result of Embodiment 1;
and
FIG. 37 is a graph showing an experimental result of Embodiment
1.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment Modes
Hereinafter, embodiment modes and an embodiment of the present
invention will be explained with reference to the drawings. Note
that it is easily understood by those skilled in the art that forms
and details of the invention can be variously changed without
departing from the spirit and scope of the invention. Therefore,
the present invention should not be construed as being limited to
the content of the embodiment modes. Note that common portions and
portions having similar functions are denoted by the same reference
numerals in all diagrams for describing embodiment modes, and
description thereof will not be repeated.
Embodiment Mode 1
In this embodiment mode, a concept of a display device in which a
pair of stacked layers each including a polarizer using the present
invention is provided will be explained.
FIG. 1A is a cross-sectional view of a display device having a pair
of stacked layers each including a polarizer, in which the wave
length distributions of the extinction coefficients with respect to
the absorption axes are different, and a structure in which at
least one of the layers having the polarizers is disposed so as to
be deviated from a parallel Nicols state. FIG. 1B is a perspective
view of the display device. In this embodiment mode, an example of
a liquid crystal display device having a liquid crystal element as
a display element will be described.
As shown in FIG. 1A, a layer 100 having a liquid crystal element is
sandwiched between a first substrate 101 and a second substrate 102
which are arranged so as to face each other.
In this embodiment mode, stacked layers each including a polarizer
are provided on an outer side of a substrate, where the substrate
is not in contact with a layer having a liquid crystal element.
Specifically, as shown in FIG. 1A, a first layer 103 including a
polarizer and a second layer 104 including a polarizer are provided
on a first substrate 101 side. Meanwhile, a third layer 105
including a polarizer and a fourth layer 106 including a polarizer
are provided on a second substrate 102 side. In this embodiment
mode, in a pair of layers each including a polarizer, in which the
wavelength distributions of the extinction coefficients with
respect to the absorption axes are different, at least one of the
stacked layers each including a polarizers is deviated from a
parallel Nicols state. Specifically, as shown in FIG. 1B, the first
layer 103 including a polarizer and the second layer 104 including
a polarizer are stacked so that the absorption axis (A) of the
first layer 103 and the absorption axis (B) of the second layer 104
where the wavelength distributions of the extinction coefficients
are different are deviated from a parallel state. Further, the
third layer 105 including a polarizer and the fourth layer 106
including a polarizer are stacked so that the absorption axis (C)
of the third layer 105 and the absorption axis (D) of the fourth
layer 106 where the wavelength distributions of the extinction
coefficients are different are in parallel, that is, in a parallel
Nicols state.
A polarizer has inconstant dependence of the absorption properties
on a wavelength, and the absorption properties with respect to a
certain wavelength region are lower than that with respective to
another wavelength region, that is, the polarizer has properties of
hardly absorbing light of the certain wavelength region.
Accordingly, even when a plurality of polarizers of the same type
is used in attempting to improve contrast ratio, a certain
wavelength region of light which is hardly absorbed remains. In
accordance with the present invention, the wavelength region of
light which is hardly absorbed can be eliminated or reduced by
combining and stacking polarizers where the wavelength
distributions of the extinction coefficients with respect to the
absorption axis are different. Therefore, even slight light leakage
can be prevented, and contrast ratio can be further improved.
Each of the substrates is a light-transmitting insulating substrate
(hereinafter also referred to as a light-transmitting substrate).
The substrate is especially transparent to light in the visible
wavelength range. As the substrates, for example, a glass substrate
made of barium borosilicate glass, aluminoborosilicate glass, or
the like; a quartz substrate; or the like can be used.
Alternatively, a substrate formed of plastic typified by
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
and polyether sulfone (PES), or a flexible synthetic resin such as
acrylic can be used as the substrates. Further, a film (formed of
polypropylene, polyester, vinyl, polyvinyl fluoride, polyvinyl
chloride, or the like), a base film (formed of polyester or
polyamide, an inorganic deposition film, or the like) may be used
as the substrates.
Further, although not shown in FIGS. 1A and 1B, an irradiation
means such as a backlight is disposed below the fourth layer 106
including the polarizer.
In this embodiment mode, the first layer 103 including the
polarizer and the third layer 105 including the polarizer are
arranged so as to be in a crossed Nicols state. The first layer 103
including the polarizer and the third layer 105 including the
polarizer may be deviated from the crossed Nicols state within the
range where predetermined black display is obtained.
FIG. 5 is a top view of angles between the absorption axis (A) of
the first layer 103 including the polarizer, the absorption axis
(B) of the second layer 104 including the polarizer, the absorption
axis (C) of the third layer 105 including the polarizer, and the
absorption axis (D) of the fourth layer 106 including the
polarizer. The first layer 103 including the polarizer and the
second layer 104 including the polarizer are stacked in such a way
that the absorption axis (A) and the absorption axis (B) are
deviated by an angle .theta.. In this embodiment mode, the third
layer 105 including the polarizer and the fourth layer 106
including the polarizer are arranged in such a way that the
absorption axis (C) and the absorption axis (D) are in a parallel
Nicols state.
Note that a polarizer characteristically has a transmission axis
perpendicular to the absorption axis. Therefore, a state where the
transmission axes are parallel to each other can also be referred
to as a parallel Nicols state, and a state where transmission axes
are perpendicular to each other can also be referred to as a
crossed Nicols state.
Note that the number of the stacked layers each including a
polarizer a having different wavelength distribution of extinction
coefficient from each other in FIGS. 1A and 1B is two; however, the
present invention is not limited thereto and a multilayer structure
having more than two layers may be used. An example of further
stacking a fifth layer 121 including a polarizer over the first
layer 103 including a polarizer and the second layer 104 including
the polarizer which have different wavelength distributions of
extinction coefficients is shown in FIGS. 7A and 7B. In FIGS. 7A
and 7B, the fifth layer 121 including the polarizer has an
absorption axis (G), and the absorption axis (G) is parallel to the
absorption axis (B) of the second layer 104 including the
polarizer, and deviated from the absorption axis (A) of the first
layer 103 including the polarizer. In other words, as shown in FIG.
6A, the fifth layer 121 including the polarizer and the second
layer 104 including the polarizer are stacked so that their
absorption axes are in a parallel Nicols state.
Further, the wavelength distribution of the extinction coefficient
with respect to the absorption axis of the fifth layer 121
including the polarizer may be equal to or different from that with
respect to the first layer 103 including the polarizer or the
second layer 104 including the polarizer which is to be stacked
together therewith. In this embodiment mode, the wavelength
distribution of the extinction coefficient with respect to the
absorption axis of the fifth layer 121 including the polarizer is
different from that with respect to those of the first layer 103
including the polarizer and the second layer 104 including the
polarizer. Thus, when the wavelength distributions of the
extinction coefficients with respect to the absorption axes of the
polarizers in the stacked layers are different, the wavelength
range of light which can be absorbed can be extended; thus, even
slight light leakage can be prevented. In the present invention, a
stack in which absorption axes of the polarizers are deviated from
a parallel Nicols state may be used in a plurality of stacked
layers each including a polarizer. Similarly, at least two
polarizers having different wavelength distributions of extinction
coefficients may be used in a plurality of stacked layers each
including a polarizer.
Further, a fifth layer including a polarizer may be provided
between the first layer 103 including the polarizer and the second
layer 104 including the polarizer in such a manner the fifth layer
and the first layer 103 are in a parallel Nicols state. FIGS. 8A
and 8B show an example in which a fifth layer 122 including a
polarizer is stacked between the first layer 103 including the
polarizer and the second layer 104 including the polarizer. In FIG.
8, the fifth layer 122 including the polarizer has an absorption
axis (H), and the absorption axis (H) is parallel to the absorption
axis (A) of the first layer 103 including the polarizer, and
deviated from the absorption axis (B) of the second layer 104
including the polarizer. Accordingly, as shown in FIG. 6B, the
fifth layer 122 including the polarizer, the first layer 103
including the polarizer, and the second layer 104 including the
polarizer are stacked so that the absorption axes of the fifth
layer 122 and the first layer 103 are in a parallel Nicols state,
and the absorption axes of the fifth layer 122 and the second layer
104 are deviated by a deviated angle .theta..
Further, the stack including the third layer 105 including the
polarizer and the fourth layer 106 including the polarizer which
are stacked in a parallel Nicols state on a light source side may
be replaced by one layer (See FIG. 31). In that case, a stack
including the first layer 103 including the polarizer and the
second layer 104 including the polarizer having a different
wavelength distribution of extinction coefficient from each other
is disposed on the viewing side, and the third layer 105 including
the polarizer is disposed on the light source side with a layer
including a liquid crystal element therebetween. The structure as
shown in FIG. 31 may preferably be used when the amount of light
from the light source is desired not to decrease.
As in this embodiment mode, a pair of stacked layers including
polarizers can be applied to a display device where light can be
extracted from both sides of a substrate.
Thus, in a pair of stacked layers each including polarizers,
polarizers in at least one of the layers each including polarizers
having different wavelength distributions of extinction
coefficients, preferably, the layer on a viewing side, are provided
so that the absorption axes of the polarizers are deviated from a
parallel Nicols state, thereby reducing light leakage in the
directions of the absorption axes. Thus, contrast ratio of the
display device can be increased.
Embodiment Mode 2
This embodiment mode will describe a concept of a display device
provided with a retardation plate in addition to a pair of stacked
layers each including a polarizing plate having a different
wavelength distribution of extinction coefficient from each other
with respect to the absorption axes unlike the above embodiment
mode.
FIG. 2A is a cross-sectional view of a display device in which one
of the pair of stacked layers each including a polarizer having a
different wavelength distribution of extinction coefficient from
each other with respect to the absorption axis is stacked to be
deviated from a parallel Nicols state, and retardation plates are
provided between the pair of stacked layers each including a
polarizer and substrates respectively, while FIG. 2B is a
perspective view of the display device. In this embodiment mode, a
liquid crystal display device having a liquid crystal element as a
display element will be explained as an example.
As shown in FIG. 2A, a layer 100 including a liquid crystal element
is sandwiched between a first substrate 101 and a second substrate
102 which are disposed to face each other.
As shown in FIG. 2A, a first layer 103 including a polarizer and a
second layer 104 including a polarizer are provided on a first
substrate 101 side. A third layer 105 including a polarizer and a
fourth layer 106 including a polarizer are provided on a second
substrate 102 side.
As shown in FIG. 2B, the first layer 103 including the polarizer
and the second layer 104 including the polarizer are arranged so
that the absorption axes of the polarizing plate having different
wavelength distributions of extinction coefficients are deviated
from a parallel Nicols state. Further, a retardation plate 113 is
provided between the stacked layers each including the polarizing
plate having a different wavelength distribution of extinction
coefficient from each other with respect to the absorption axes and
the first substrate 101.
Further, as shown in FIG. 2B, the third layer 105 including the
polarizer and the fourth layer 106 including the polarizer are
provided on the second substrate 102 side. The third layer 105
including the polarizer and the fourth layer 106 including the
polarizer are arranged to be in a parallel Nicols state. In
addition, a retardation plate 114 is provided between the stacked
layers each including the polarizer and the second substrate
102.
In addition, although not shown in FIGS. 2A and 2B, an irradiation
means such as a backlight is disposed below the fourth layer 106
including the polarizer.
The retardation plate may be, for example, a film in which liquid
crystals are hybrid-aligned, a film in which liquid crystals are
twist-aligned, a uniaxial retardation plate, or a biaxial
retardation plate. Using such retardation plates, the viewing angle
of the display device can be extended. The film in which liquid
crystals are hybrid-aligned is a compound film in which a triacetyl
cellulose (TAC) film is used as a base and discotic liquid crystals
having negative uniaxiality are hybrid-aligned to obtain optical
anisotropy.
The uniaxial retardation plate is formed by stretching a resin in
one direction. Meanwhile, a biaxial retardation plate is formed by
stretching a resin into an axis in a crosswise direction, and then
gently stretching the resin into an axis in a lengthwise direction.
The resin used here may be cyclo-olefin polymer (COP),
polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene
(PS), polyether sulfone (PES), polyphenylene sulfide (PPS),
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
polypropylene (PP), polyphenylene oxide (PPO), polyarylate (PAR),
polyimide (PI), polytetrafluoroethylene (PTFE), or the like.
The film in which liquid crystals are hybrid-aligned is a film
formed by using a triacetyl cellulose (TAC) film as a base and
hybrid-aligning discotic liquid crystals or nematic liquid crystal
molecules. The retardation plate can be attached to a
light-transmitting substrate after being attached to a layer
including a polarizer.
Circular polarization, elliptical polarization, or the like can be
performed by combining a retardation plate and stacked polarizers.
Further, a plurality of retardation plates may be used instead of
one polarizer. Note that a retardation plate characteristically has
a fast axis perpendicular to a slow axis. Therefore, the
arrangement can be determined based on fast axes instead of slow
axes.
Note that in this embodiment mode, the first layer 103 including
the polarizer and the third layer 105 including the polarizer are
arranged to be in a crossed Nicols state. The first layer 103
including the polarizer and the third layer 105 including the
polarizer may be deviated as long as display of a predetermined
black level can be obtained.
Note that the number of the stacked layers each including a
polarizer having a different wavelength distribution of extinction
coefficient from each other in FIGS. 2A and 2B is two; however, the
present invention is not limited thereto and a multilayer structure
having more than two layers may be used. A fifth layer including a
polarizer may be provided between the first layer 103 including the
polarizer and the second layer 104 including the polarizer in such
a manner the fifth layer and the first layer 103 are in a parallel
Nicols state. An example of further stacking a fifth layer 122
including a polarizer over the first layer 103 including a
polarizer and the second layer 104 including the polarizer is shown
in FIGS. 11A and 11B. In FIGS. 11A and 11B, the fifth layer 122
including the polarizer has an absorption axis (H), and the
absorption axis (H) is parallel to the absorption axis (A) of the
first layer 103 including the polarizer, and deviated from the
absorption axis (B) of the second layer 104 including the
polarizer. Accordingly, the fifth layer 122 including the
polarizer, the first layer 103 including the polarizer, and the
second layer 104 including the polarizer are stacked so that the
absorption axes of the fifth layer 122 and the first layer 103 are
in a parallel Nicols state, and the absorption axes of the fifth
layer 122 and the second layer 104 are deviated by a deviated angle
.theta..
Further, the wavelength distribution of the extinction coefficient
with respect to the absorption axis of the fifth layer 122
including the polarizer may be equal to or different from that with
respect to the first layer 103 including the polarizer or the
second layer 104 including the polarizer which is to be stacked
together therewith. In this embodiment mode, the wavelength
distribution of the extinction coefficient with respect to the
absorption axis of the fifth layer 122 including the polarizer is
different from that with respect to those of the first layer 103
including the polarizer and the second layer 104 including the
polarizer. Thus, when the wavelength distributions of the
extinction coefficients with respect to the absorption axes of the
polarizers in the stacked layers are different, the wavelength
range of light which can be absorbed can be extended; thus, even
slight light leakage can be prevented.
As in this embodiment mode, a pair of stacked layers each including
polarizers can be applied to a display device where light can be
extracted from both sides of a substrate.
Thus, in a structure having a pair of stacked layers each including
polarizers and a retardation plate, polarizers in at least one of
the layers each including polarizers having different wavelength
distributions of extinction coefficients, preferably, the layer on
a viewing side, are provided so that their absorption axes are
deviated from a parallel Nicols state, thereby reducing light
leakage in the directions of the absorption axes. Thus, contrast
ratio of the display device can be increased.
Embodiment Mode 3
This embodiment mode will describe a concept of a display device
provided with stacked layers each including a polarizing plate
having a different wavelength distribution of extinction
coefficient from each other with respect to the absorption axes
unlike the above embodiment mode. The like parts or parts having
like functions are denoted by the same reference numerals, and the
description of them will not be repeated.
FIG. 3A is a cross-sectional view of a display device having
stacked layers including polarizers, which are arranged to be
deviated from a parallel Nicols state, and FIG. 3B shows a
perspective view of the display device. In this embodiment mode, an
example of a liquid crystal display device including a liquid
crystal element as a display element will be described.
As shown in FIG. 3A, a layer 100 including a liquid crystal element
is sandwiched between a first substrate 101 and a second substrate
102 which are disposed to face each other.
Stacked layers each including a polarizer are provided on an outer
side of a substrate, where the substrate is not in contact with a
layer having a liquid crystal element. A first layer 103 including
a polarizer and a second layer 104 including a polarizer are
provided on a first substrate 101 side. Here, the first layer 103
including the polarizer and the second layer 104 including the
polarizer are arranged so that their absorption axes are deviated
to be in a parallel Nicols state. In this embodiment mode, the
wavelength distributions of the extinction coefficients of the
polarizers in the first layer 103 and the second layer 104 with
respect to the absorption axes are different from each other.
In this embodiment mode, a reflector plate may be provided in
addition. The reflector plate can be provided by forming a pixel
electrode from a highly reflective material on an outer side of the
second substrate 102.
As shown in FIG. 3B, the first layer 103 including the polarizer
having an absorption axis (A) and the second layer 104 including a
polarizer having an absorption axis (B) are stacked so that their
absorption axes are deviated from each other. Thus, when layers
including polarizers are stacked so that their absorption axes are
deviated, contrast ratio can be increased.
Further, even when a plurality of polarizers of the same type is
used in attempting to improve contrast ratio, a certain wavelength
region of light which is hardly absorbed remains. In accordance
with the present invention, the wavelength region of light which is
hardly absorbed can be eliminated or reduced by combining and
stacking polarizers where the wavelength distributions of the
extinction coefficients with respect to the absorption axis are
different. Therefore, even slight light leakage can be prevented,
and contrast ratio can be further improved.
FIG. 3C illustrates an angle formed between the absorption axis (A)
of the polarizer included in the first layer 103 and the absorption
axis (B) of the polarizer included in the second layer 104, which
is viewed from above. The first layer 103 including the polarizer
and the second layer 104 including the polarizer are stacked in
such a way that the absorption axis (A) and the absorption axis (B)
are deviated by an angle of .theta..
Note that the number of the stacked layers each including a
polarizer having a different wavelength distribution of extinction
coefficient from each other in FIGS. 3A to 3C is two; however, the
present invention is not limited thereto and a multilayer structure
having more than two layers may be used. An example of further
stacking a fifth layer 121 including a polarizer over the first
layer 103 including a polarizer and the second layer 104 including
the polarizer is shown in FIGS. 11A to 11C. In FIGS. 11A and 11B,
the fifth layer 121 including the polarizer has an absorption axis
(G), and the absorption axis (G) is parallel to the absorption axis
(B) of the second layer 104 including the polarizer, and deviated
from the absorption axis (A) of the first layer 103 including the
polarizer. In other words, as shown in FIG. 9C, the fifth layer 121
including the polarizer and the second layer 104 including the
polarizer are stacked so that their absorption axes are in a
parallel Nicols state.
Further, a fifth layer including a polarizer may be provided
between the first layer 103 including the polarizer and the second
layer 104 including the polarizer in such a manner the fifth layer
and the first layer 103 are in a parallel Nicols state. FIGS. 10A
to 10C show an example in which a fifth layer 122 including a
polarizer is stacked between the first layer 103 including the
polarizer and the second layer 104 including the polarizer. In
FIGS. 10A and 10B, the fifth layer 122 including the polarizer has
an absorption axis (H), and the absorption axis (H) is parallel to
the absorption axis (A) of the first layer 103 including the
polarizer, and deviated from the absorption axis (B) of the second
layer 104 including the polarizer. Accordingly, as shown in FIG.
10C, the fifth layer 122 including the polarizer, the first layer
103 including the polarizer, and the second layer 104 including the
polarizer are stacked so that the absorption axes of the fifth
layer 122 and the first layer 103 are in a parallel Nicols state,
and the absorption axes of the fifth layer 122 and the second layer
104 are deviated by a deviated angle .theta..
Further, the wavelength distribution of the extinction coefficient
with respect to the absorption axis of the fifth layer 122
including the polarizer may be equal to or different from that with
respect to the first layer 103 including the polarizer or the
second layer 104 including the polarizer which is to be stacked
together therewith. In this embodiment mode, the wavelength
distribution of the extinction coefficient with respect to the
absorption axis of the fifth layer 122 including the polarizer is
different from that with respect to those of the first layer 103
including the polarizer and the second layer 104 including the
polarizer. Thus, when the wavelength distributions of the
extinction coefficients with respect to the absorption axes of the
polarizers in the stacked layers are different, the wavelength
range of light which can be absorbed can be extended; thus, even
slight light leakage can be prevented.
As in this embodiment mode, the structure in which layers including
polarizers are stacked over one side of a substrate can be applied
to a display device where light can be extracted from one sides of
a substrate.
Thus, the layers each including a polarizer having a different
wavelength distribution of extinction coefficient from each other
are provided so that their absorption axes are deviated from a
parallel Nicols state, thereby reducing light leakage in the
directions of the absorption axes. Thus, contrast ratio of the
display device can be increased.
Embodiment Mode 4
This embodiment mode will describe a concept of a display device
provided with a retardation plate in addition to layers each
including a polarizing plate having a different wavelength
distribution of extinction coefficient from each other with respect
to the absorption axes, which are stacked on a viewing side unlike
the above embodiment mode. The like parts or parts having like
functions are denoted by the same reference numerals, and the
description of them will not be repeated.
FIG. 4A is a cross-sectional view of a display device in which a
retardation plate is provided between a substrate and layers
including a polarizers which are stacked to be deviated from a
parallel Nicols state, and FIG. 4B is a perspective view of the
display device. In this embodiment mode, an example of a liquid
crystal display device including a liquid crystal element as a
display element will be described.
As shown in FIG. 3A, a layer 100 including a liquid crystal element
is sandwiched between a first substrate 101 and a second substrate
102 which are disposed to face each other.
As shown in FIG. 4B, the first layer 103 including the polarizer
and the second layer 104 including the polarizer are provided on
the first substrate 101 side. Here, the first layer 103 including
the polarizer and the second layer 104 including the polarizer are
arranged to be deviated from a parallel Nicols state. In addition,
a retardation plate 113 is provided between the first substrate 101
and the stacked layers each including the polarizer. In this
embodiment mode, the wavelength distributions of the extinction
coefficients of the polarizers in the first layer 103 and the
second layer 104 with respect to the absorption axes are different
from each other.
In this embodiment mode, a reflector plate may be provided in
addition. The reflector plate can be provided by forming a pixel
electrode from a highly reflective material on an outer side of the
second substrate 102.
As shown in FIG. 4B, the first layer 103 including the polarizer
having an absorption axis (A) and the second layer 104 including a
polarizer having an absorption axis (B) are stacked so that their
absorption axes are deviated from each other. Further, the
absorption axis (A) of the polarizer included in the first layer
103 may preferably be arranged to be deviated from the slow axis of
the retardation plate 113 by 45.degree.. Thus, when layers
including polarizers are stacked so that their absorption axes are
deviated and a retardation plate is provided, contrast ratio can be
increased.
Note that the number of the stacked layers each including a
polarizer having a different wavelength distribution of extinction
coefficient from each other in FIGS. 4A and 4B is two; however, the
present invention is not limited thereto and a multilayer structure
having more than two layers may be used. An example of further
stacking a fifth layer 122 including a polarizer over the first
layer 103 including a polarizer and the second layer 104 including
the polarizer is shown in FIGS. 12A to 12C. In FIGS. 12A and 12B,
the fifth layer 122 including the polarizer has an absorption axis
(G), and the absorption axis (G) is parallel to the absorption axis
(B) of the second layer 104 including the polarizer, and deviated
from the absorption axis (A) of the first layer 103 including the
polarizer. In other words, the fifth layer 122 including the
polarizer and the second layer 104 including the polarizer are
stacked so that their absorption axes are in a parallel Nicols
state.
Further, the wavelength distribution of the extinction coefficient
with respect to the absorption axis of the fifth layer 122
including the polarizer may be equal to or different from that with
respect to the first layer 103 including the polarizer or the
second layer 104 including the polarizer which is to be stacked
together therewith. In this embodiment mode, the wavelength
distribution of the extinction coefficient with respect to the
absorption axis of the fifth layer 122 including the polarizer is
different from that with respect to those of the first layer 103
including the polarizer and the second layer 104 including the
polarizer. Thus, when the wavelength distributions of the
extinction coefficients with respect to the absorption axes of the
polarizers in the stacked layers are different, the wavelength
range of light which can be absorbed can be extended; thus, even
slight light leakage can be prevented.
As in this embodiment mode, the structure in which layers including
polarizers are stacked over one side of a substrate can be applied
to a display device where light can be extracted from one sides of
a substrate.
Thus, the layers each including a polarizer having a different
wavelength distribution of extinction coefficient from each other
are provided so that their absorption axes are deviated from a
parallel Nicols state and a retardation plate is provided in
addition, thereby reducing light leakage in the directions of the
absorption axes. Thus, contrast ratio of the display device can be
increased.
Embodiment Mode 5
In this embodiment mode, structures of polarizers having different
wavelength distributions of extinction coefficients with respect to
the absorption axes are different from each other which can be used
for the present invention will be described with reference to FIGS.
13A to 13C.
In the present invention, a layer including a polarizer includes at
least a polarizer having a specific absorption axis. A single layer
polarizer, or a polarizer inserted between protective layers may be
used. FIGS. 13A to 13C illustrate examples of layered structures of
layers including polarizers in accordance with the present
invention. In FIG. 13A, a layer including a polarizer having a
protective layer 50a, a first polarizer 51, and a protective layer
50b is stacked together with a layer including a polarizer having a
protective layer 50c, a second polarizer 52, and a protective layer
50d and the stack constitutes a layer including stacked polarizers.
Thus, in the present invention, "stacked polarizers" includes a
stack including polarizers in which a protective layer is
interposed therebetween, where the polarizers are not stacked in
contact with each other. Accordingly "a layer including stacked
polarizers" may mean the whole stack including the layer including
the polarizer having the protective layer 50a, the first polarizer
51, and the protective layer 50b and a layer including the
polarizer having the protective layer 50c, the second polarizer 52,
and the protective layer 50d. Further, in this specification, the
layer including a polarizer having the protective layer 50a, the
first polarizer 51, and the protective layer 50b is also referred
to as a polarizing plate. Therefore, what is shown in FIG. 13A can
also be referred to as a stack including polarizing plates. In FIG.
13A, the first polarizer 51 and the second polarizer 52 are stacked
so that their absorption axes are deviated from each other.
Further, wavelength distributions of extinction coefficients with
respect to the absorption axes of the first polarizer 51 and the
second polarizer 52 are different from each other.
FIG. 13B shows a layer including stacked polarizers, which is a
stack having a protective layer 56a, a first polarizer 57, a second
polarizer 58, and a protective layer 56b. The structure shown in
FIG. 13B can be expressed as "a stack of the protective layer 56a
and the protective layer 56b is provided so that the stacked
polarizers including the first polarizer 57 and the second
polarizer 58 are provided therebetween", or as "a layer including a
polarizer having the protective layer 56a and the polarizer 57 is
stacked together with a layer including a polarizer having the
polarizer 58 and the protective layer 56b". FIG. 13B shows an
example in which polarizers are directly stacked without protective
layers therebetween unlike in FIG. 13A. This structure has an
advantage in that the layer including stacked polarizers which is a
polarizing means can be made thinner, and the number of stacked
protective layers may be small; thus, the process can be simplified
at low cost. In FIG. 13B, the first polarizer 57 and the second
polarizer 58 are stacked so that their absorption axes are deviated
from each other. Further, the wavelength distributions of the
extinction coefficients with respect to the absorption axes of the
first polarizer 57 and the second polarizer 58 are different from
each other.
FIG. 13C shows a structure in which polarizers are stacked together
with one protective layer therebetween, which is in between the
structures shown in FIG. 13A and FIG. 13B. FIG. 13C shows a layer
including stacked polarizers, which is a stack including a
protective layer 60a, a first polarizer 61, a protective layer 60b,
a second polarizer 62, and a protective layer 60c. Such a structure
in which protective layers and polarizers are stacked alternately
may be used. A polarizer in the present invention is in a film
form, and can be referred to as a polarizing film or a polarizing
layer. In FIG. 13C, the first polarizer 61 and the second polarizer
62 are stacked so that their absorption axes are deviated from each
other. In addition, wavelength distributions of extinction
coefficients with respect to the absorption axes of the first
polarizer 61 and the second polarizer 62 are different from each
other.
FIGS. 13A to 13C show examples of stacking two layers of
polarizers; however, three layers of polarizers may be stacked, or
a greater number of layers of polarizers may be provided. The
manner of providing protective layers is also not limited to the
structures shown in FIG. 13A to 13C. Further, a structure may be
used in which the layer including the stacked polarizers in FIG.
13A is stacked together with the layer including the stacked
polarizers in FIG. 13B. In the case of polarizers which easily
deteriorate due to moisture or temperature change depending on the
material of the polarizer, the polarizers can be protected by
covering the polarizers as shown in FIG. 13A; thus, reliability can
be improved. As shown in FIG. 1, in the case of providing
polarizers so as to interpose a layer including a display element
therebetween, the layered structure of the polarizers on a viewing
side ma be the same as or different from the layered structure of
the polarizers on the opposite side opposite with the display
element in-between. Thus, the layered structure of the stacked
polarizers may be set as appropriate depending on the properties of
the polarizers and functions required for the display device. For
example, in Embodiment Mode 1, each of the layers including the
polarizers 103 and 104, and the layer including the polarizers 105
and 106 constitutes a layer including stacked polarizers; however,
the layers may have any of the structures shown in FIGS. 13A to
13C, or one of the layers may have the structure in FIG. 13A and
the other has the structure shown in FIG. 13B.
Further, the layers including stacked polarizers may have a
structure in which bonding layers (adhesive layers) are provided
between protective layers, between polarizers, and between the
protective layer and the polarizer to bond them. In this case, the
adhesion layers are required to have light-transmitting properties
as the protective layers have. A retardation plate may be stacked
together with a polarizer. The retardation plate also may have a
structure in which a retardation film is provided between a pair of
protective layers and may be stacked together with a polarizer with
one or a plurality of protective layers in-between, or may be
directly stacked together with the polarizer so that a protective
layer, a retardation film, a polarizer, and a protective layer are
sequentially stacked together. For example, in FIG. 13B, when the
protective layer 56a is on a light-transmitting substrate side, a
retardation film may be provided between the protective layer 56a
and the polarizer 57, and another retardation film is provided
between the light-transmitting substrate and the polarizer.
Further, a more durable protective film or the like may be provided
for example as a surface protective layer on the protective layer
50d. Further, an anti-reflective film which prevents reflection of
external light on a screen surface or an antiglare film which
prevents glare or dazzle on a screen may be provided. Further, when
a layer including a polarizer (polarizing plate) is bonded to a
substrate, an adhesion layer of an acrylic adhesive or the like may
be used.
The polarizer transmits only light vibrating in a certain direction
and absorbs other light. A uniaxially stretched resin film to which
dichromatic pigment is adsorbed and oriented can be used. As the
resin, PVA (polyvinyl alcohol) can be used. PVA has high
transparency and intensity, and can be easily attached to TAC
(triacetyl cellulose) that is used as a protective layer (also
referred to as a protective film because of its shape). As the
pigment, iodine-based pigment and dye-based pigment can be used.
For example, in a case of iodine-based pigment, iodine having high
dichroism is adsorbed as a high ion to a PVA resin film and
stretched in a boric acid aqueous solution, whereby the iodine is
arranged as a chain polymer, and a polarizer shows a high
polarizing characteristic. On the other hand, dye-based pigment in
which dye having high dichroism is used instead of iodine has
superiority in heat resistance and durability.
The protective layer reinforces intensity of the polarizer and
prevents deterioration due to the temperature and moisture. As the
protective layer, a film such as a TAC (triacetyl cellulose) film,
a COP (cyclic olefin polymer-based) film, a PC (polycarbonate) film
can be used. TAC has transparency, low birefringence, and
superiority in an adhesive property to PVA that is used for the
polarizer. COP is a resin film having superiority in heat
resistance, moisture resistance, and durability. Further,
iodine-based pigment and dye-system pigment can be mixed to be
used.
As for the layer including a polarizer, for example, an adhesive
surface, TAC (triacetyl cellulose) that is a protective layer, a
mixed layer of iodine and PVA (polyvinyl alcohol) that is a
polarizer, and TAC that is a protective layer are sequentially
stacked from a substrate side. The polarization degree can be
controlled by the mixed layer of iodine and PVA (polyvinyl
alcohol). Alternatively, an inorganic material may be used for a
polarizer. The layer including a polarizer may be referred to as a
polarizing plate because of its shape.
This embodiment mode can be used in combination with any one of the
above embodiment modes.
Thus, polarizers having different wavelength distributions of
extinction coefficients from each other are stacked so that their
absorption axes are deviated from a parallel Nicols state, thereby
reducing light leakage in the directions of the absorption axes.
Thus, contrast ratio of the display device can be increased.
Embodiment Mode 6
In this embodiment mode, a structure of a liquid crystal display
device having a pair of stacked layers each including a polarizer
having different wavelength distribution of extinction coefficient
with respect to the absorption axes with each other will be
explained, in which polarizers of at least one of the pars of the
stacked layers each including a polarizer are arranged so that the
transmission axes are deviated from each other.
FIG. 16A is a top view showing a structure of a display panel in
accordance with the present invention, where a pixel portion 2701
in which pixels 2702 are arranged in matrix, a scanning line input
terminal 2703, and a signal line input terminal 2704 are formed
over a substrate 2700 having an insulating surface. The number of
pixels may be provided according to various standards: the number
of pixels of XGA for RGB full-color display may be
1024.times.768.times.3 (RGB), that of UXGA for RGB full-color
display may be 1600.times.1200.times.3 (RGB), and that
corresponding to a full-speck high vision for RGB full-color
display may be 1920.times.1080.times.3 (RGB).
The pixels 2702 are arranged in matrix by intersecting scanning
lines extended from the scanning line input terminal 2703 with
signal lines extended from the signal line input terminal 2704.
Each pixel 2702 is provided with a switching element and a pixel
electrode layer connected to the switching element. A typical
example of the switching element is a TFT. A gate electrode layer
side of the TFT is connected to the scanning line, and a source or
drain side thereof is connected to the signal line, thereby each
pixel can be controlled independently by a signal inputted from the
external.
FIG. 16A shows a structure of the display panel in which signals
inputted to a scanning line and a signal line are controlled by an
external driver circuit. Alternatively, driver ICs 2751 may be
mounted on the substrate 2700 by COG (Chip on Glass) as shown in
FIG. 17A. Further, the driver ICs may also be mounted by TAB (Tape
Automated Bonding) as shown in FIG. 17B. The driver ICs may be one
formed over a single crystalline semiconductor substrate or may be
a circuit that is formed using a TFT over a glass substrate. In
FIGS. 17A and 17B, each driver IC 2751 is connected to an FPC
(Flexible printed circuit) 2750.
Further, in the case where a TFT provided in a pixel is formed
using a semiconductor having crystallinity, a scanning line driver
circuit 3702 can also be formed over a substrate 3700 as shown in
FIG. 16B. In FIG. 16B, a pixel portion 3701 connected to a signal
line input terminal 3704 is controlled by an external driver
circuit similarly to that in FIG. 16A. In a case where a TFT
provided in a pixel is formed using a polycrystalline
(microcrystalline) semiconductor, a single crystalline
semiconductor, or the like with high mobility, a pixel portion
4701, a scanning line driver circuit 4702, and a signal line driver
circuit 4704 can be formed over a substrate 4700 in an integrated
manner in FIG. 16C.
FIG. 14A is a top view of a liquid crystal display device that has
a stacked layer including a polarizer, and FIG. 14B is a
cross-sectional view taken along a line C-D of FIG. 14A.
As shown in FIG. 14A, a pixel portion 606, a driver circuit area
608a which is a scan line driver circuit, and a driver circuit area
608b which is a scan line driver circuit are sealed with a sealant
692 between a substrate 600 and an opposite substrate 695. A driver
circuit area 607 which is a signal line driver circuit formed by an
IC driver is provided over the substrate 600. The pixel portion 606
is provided with a transistor 622 and a capacitor element 623, and
the driver circuit area 608b is provided with a driver circuit
including a transistor 620 and a transistor 621. An insulating
substrate similar to that of the above embodiment mode can be
applied to the substrate 600. It is a concern that a substrate made
from a synthetic resin generally has a lower allowable heat
resistance temperature compared to other substrates; however, it
can be employed by being deviated after a manufacturing process
using a substrate with higher heat resistance.
In the pixel portion 606, the transistor 622 that is to be a
switching element through base insulating films 604a and 604b is
provided. In this embodiment mode, a multi-gate thin film
transistor (TFT) is used for the transistor 622, which includes a
semiconductor layer having an impurity region serving as a source
region and a drain region, a gate insulating layer, a gate
electrode layer having a stacked-layer structure made of two
layers, a source electrode layer, and a drain electrode layer. The
source electrode layer or the drain electrode layer is electrically
connected so as to be in contact with the impurity region of the
semiconductor layer and a pixel electrode layer 630. The thin film
transistor can be manufactured by various methods. For example, a
crystalline semiconductor film is applied as an active layer. A
gate electrode is provided over the crystalline semiconductor film
through a gate insulating film. An impurity element can be added to
the active layer using the gate electrode. Addition of the impurity
element using the gate electrode makes it unnecessary to form a
mask for addition of the impurity element. The gate electrode can
have either a single-layer structure or a stacked-layer structure.
The impurity region can be made a high concentration impurity
region or a low concentration impurity region by controlling the
concentration thereof. A structure of such a thin film transistor
having such a low concentration impurity region is referred to as
an LDD (Lightly doped drain) structure. In addition, the low
concentration impurity region can be formed to be overlapped with
the gate electrode. A structure of such a thin film transistor is
referred to as a GOLD (Gate Overlapped LDD) structure. Polarity of
the thin film transistor is to be an n-type by using phosphorus (P)
or the like in the impurity region. When polarity of the thin film
transistor is to be a p-type, boron (B) or the like may be added.
After that, an insulating film 611 and an insulating film 612
covering the gate electrode and the like are formed. A dangling
bond of the crystalline semiconductor film can be terminated by a
hydrogen element mixed into the insulating film 611 (and the
insulating film 612).
In order to improve planarity, an insulating film 615 and an
insulating film 616 may be formed as an interlayer insulating film.
For the insulating films 615 and 616, an organic material, an
inorganic material, or a stacked structure thereof can be used. The
insulating films 615 and 616 can be formed from a material selected
from silicon oxide, silicon nitride, silicon oxynitride, silicon
nitride oxide, aluminum nitride, aluminum oxynitride, aluminum
nitride oxide or aluminum oxide containing a larger amount of
nitrogen content than oxygen content, diamond like carbon (DLC),
polysilazane, carbon containing nitrogen (CN), PSG (phosphosilicate
glass), BPSG (borophosphosilicate glass), alumina, and a substance
containing another inorganic insulating material. As the organic
material that may be either photosensitive or nonphotosensitive,
polyimide, acryl, polyamide, polyimide amide, resist,
benzocyclobutene, a siloxane resin, or the like can be used. It is
to be noted that the siloxane resin corresponds to a resin
including a Si--O--Si bond. Siloxane has a skeleton structure of a
bond of silicon (Si) and oxygen (O). As for a substituent, an
organic group containing at least hydrogen (such as an alkyl group
or aromatic hydrocarbon) is used. As for a substituent, a fluoro
group may be used. Further, as for a substituent, an organic group
containing at least hydrogen and a fluoro group may be used.
The pixel portion and the driver circuit area can be formed in an
integrated manner over the same substrate by using the crystalline
semiconductor film. In this case, the transistor in the pixel
portion and the transistor in the driver circuit area 608b are
concurrently formed. The transistor used in the driver circuit area
608b forms a CMOS circuit. Although a thin film transistor
including a CMOS circuit has a GOLD structure, an LDD structure
such as the transistor 622 may be employed.
A structure of the thin film transistor in the pixel portion is not
limited to this embodiment mode, and the thin film transistor in
the pixel portion may have a single-gate structure in which one
channel formation region is formed, a double-gate structure in
which two channel formation regions are formed, or a triple-gate
structure in which three channel formation regions are formed. A
thin film transistor in the peripheral driver circuit area may have
a single-gate structure, a double-gate structure, or a triple-gate
structure.
Further, a thin film transistor is not limited to the manufacturing
method shown in this embodiment mode. The thin film transistor may
have a top-gate structure (such as a forward stagger type), a
bottom-gate structure (such as an inverted staggered type), a
dual-gate structure in which two gate electrode layers are arranged
above and below a channel formation region through a gate
insulating film, or some other structures.
Next, an insulating layer 631 referred to as an orientation film is
formed by a printing method or a spin coating method so as to cover
the pixel electrode layer 630 and the insulating film 616. The
insulating layer 631 can be selectively formed when a screen
printing method or an off-set printing method is used. After that,
rubbing treatment is performed. When a liquid crystal mode, for
example, a VA mode, is employed, there are cases when rubbing
treatment is not performed. An insulating layer 633 serving as an
orientation film is similar to the insulating layer 631.
Subsequently, the sealant 692 is formed in the peripheral region
where the pixel is formed by a droplet discharging method.
Then, the opposite substrate 695 provided with the insulating layer
633 serving as an orientation film, a conductive layer 634 serving
as an opposite electrode, and a colored layer 635 serving as a
color filter are attached to the substrate 600 that is a TFT
substrate through a spacer 637. A liquid crystal layer 632 is
provided in a space between the substrate 600 and the opposite
substrate 695. After that, a first layer 641 including a polarizer
and a second layer 642 including a polarizer are provided on an
outer side of the opposite substrate 695. A third layer 643
including a polarizer and a fourth layer 644 including a polarizer
are provided on a side opposite to a surface having an element of
the substrate 600. The layer 643 including a polarizer and the
layer 644 including a polarizer are provided on a surface of the
substrate opposite to the surface provided with an element. Filler
may be mixed into the sealant, and the opposite substrate 695 may
be provided with a shielding film (black matrix) or the like. For a
case of full-color display of the liquid crystal display device,
the color filter or the like may be formed from a material emitting
a red color (R), a green color (G), and blue color (B). For a case
of mono-color display, the color filter or the like may be formed
from a material emitting at least one color.
When RGB light emitting diodes (LEDs) or the like are arranged in a
backlight and a successive additive color mixture method (a field
sequential method) that conducts color display by time division is
employed, there is a case when a color filter is not provided. The
black matrix may also be provided to reduce the reflection of
outside light by the wires of the transistor and the CMOS circuit.
Therefore, the black matrix is provided so as to be overlapped with
the transistor and the CMOS circuit. It is to be noted the black
matrix may also be provided so as to be overlapped with the
capacitor element. This is because the black matrix can prevent
reflection due to a metal film forming the capacitor element.
As a method for forming the liquid crystal layer, a dispenser
method (dripping method) or a dipping method (pumping method) in
which liquid crystal is injected using a capillary phenomenon after
attaching the substrate 600 having an element and the opposite
substrate 695 may be used. A dripping method may be applied when a
large-sized substrate to which it is difficult to apply an
injecting method is used.
A spacer may be provided in such a way that particles each having a
size of several .mu. meters are sprayed. In this embodiment mode, a
method is employed in which a resin film is formed over the entire
surface of the substrate and the resin film is subjected to an
etching process. The material of such a spacer is applied by a
spinner and then light-exposed and developed so that a
predetermined pattern is formed. Moreover, the spacer is heated at
150.degree. C. to 200.degree. C. in a clean oven or the like to be
hardened. The thus manufactured spacer can have various shapes
depending on the conditions of light exposure and development
processes. It is preferable that the spacer have a columnar shape
with a flat top so that mechanical intensity for the liquid crystal
display device can be secured when the opposite substrate is
attached. The shape can be conic, pyramidal, or the like without
any particular limitation.
A connection portion is formed in order to connect an external
wiring board with the inside of the display device formed in
accordance with the above-described steps. An insulating layer in
the connection portion is removed by ashing treatment using an
oxygen gas under atmospheric pressure or near atmospheric pressure.
This treatment uses an oxygen gas and one or more of hydrogen,
CF.sub.4, NF.sub.3, H.sub.2O, and CHF.sub.3. In this step, the
ashing treatment is performed after sealing with the use of the
opposite substrate in order to prevent damage or breaking due to
static electricity. If the effect by static electricity is little,
the ashing treatment may be carried out at any timing.
Subsequently, a terminal electrode layer 678 electrically connected
to the pixel portion is provided with an FPC 694, which is a wiring
board for connection, through an anisotropic conductive layer 696.
The FPC 694 is to transmit external signals or potential. Through
the above steps, a liquid crystal display device having a display
function can be manufactured.
A wiring included in the transistor, the gate electrode layer, the
pixel electrode layer 630, and the conductive layer 634 that is an
opposite electrode can be formed from a material selected from
indium tin oxide (ITO), indium zinc oxide (IZO) in which zinc oxide
(ZnO) is mixed with indium oxide, conductive materials in which
silicon oxide (SiO.sub.2) is mixed with indium oxide, organoindium,
organotin, indium oxide containing tungsten oxide, indium zinc
oxide containing tungsten oxide, indium oxide containing titanium
oxide, or indium tin oxide containing titanium oxide; a metal such
as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf),
vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt
(Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), or
copper (Cu); an alloy of such metals; or metal nitride thereof.
The substrate 600 is provided with a stacked layer of the third
layer 643 including a polarizer and the fourth layer 644 including
a polarizer. The opposite substrate 695 is provided with a stacked
layer of the first layer 641 including a polarizer and the second
layer 642 including a polarizer. The third layer 643 including a
polarizer and the fourth layer 644 including a polarizer, which are
provided on the backlight side, are arranged to be in a parallel
Nicols state. The first layer 641 including a polarizer and the
second layer 642 including a polarizer, which are provided on the
viewing side, are arranged so as to deviate from a parallel Nicols
state. The absorption axes of the polarizers of one of a pair of
the stacked polarizers, preferably the stacked polarizer on the
viewing side, are deviated, which is a feature of the present
invention. Accordingly, the contrast ratio can be enhanced. In this
embodiment mode, wavelength distributions of extinction
coefficients with respect to the absorption axes of the first layer
641 including a polarizer and the second layer 642 including a
polarizer are different from each other. Similarly, wavelength
distributions of extinction coefficients with respect to the
absorption axes of the third layer 643 including a polarizer and
the fourth layer 644 including a polarizer are different from with
each other.
The stacked layer of the third layer 643 including a polarizer and
the fourth layer 644 including a polarizer and the stacked layer of
the first layer 641 including a polarizer and the second layer 642
including a polarizer are bonded to the substrate 600 and the
opposite substrate 695, respectively. A retardation film may be
stacked to be interposed between the stacked layer including a
polarizer and the substrate.
The stacked polarizers having different wavelength distributions of
extinction coefficients are provided so that the absorption axes
thereof are arranged to be deviated from each other so as to
deviate in such a display device, thereby the contrast ratio can be
enhanced. In the present invention, a plurality of polarizers can
be made a polarizer having a staked-layer structure, which is
different from a structure in which a thickness of a polarizer is
simply made thick. The stacked polarizer deviates, thereby the
contrast ratio can be enhanced as compared with that of the
structure in which a thickness is simply made thick.
This embodiment mode can be freely combined with the above
embodiment modes.
Embodiment Mode 7
In this embodiment mode, a liquid crystal display device using a
thin film transistor that includes an amorphous semiconductor film
in addition to stacked layers each including a polarizer having a
different wavelength distribution of extinction coefficient from
each other, which is different from that of the above embodiment
modes, will be explained.
A display device shown in FIG. 15 includes a transistor 220 that is
an inversely staggered thin film transistor in a pixel portion, a
pixel electrode layer 201, an insulating layer 203, a liquid
crystal layer 204, a spacer 281, an insulating layer 205, an
opposite electrode layer 206, a color filter 208, a black matrix
207, an opposite substrate 210, a first layer 231 including a
polarizer, a second layer 232 including a polarizer, a third layer
233 including a polarizer, and a fourth layer 234 including a
polarizer over a substrate 200. In addition, the display device
also includes a sealant 282, a terminal electrode layer 287, an
anisotropic conductive layer 285, and an FPC 286 in a sealing
region.
A gate electrode layer, a source electrode layer, and a drain
electrode layer of the transistor 220 that is the inversely
staggered thin film transistor manufactured in this embodiment mode
are formed by a droplet discharging method. The droplet discharging
method is a method for discharging a composition containing a
liquid conductive material and solidifying the composition by
drying and baking, thereby a conductive layer and an electrode
layer are formed. By discharging a composition containing an
insulating material and solidifying it by drying and baking, an
insulating layer can also be formed. By the droplet discharging
method, a constituent of a display device such as a conductive
layer or an insulating layer can be selectively formed, which can
simplify the manufacturing steps and reduce the loss of materials;
thus, a display device can be manufactured at low cost with high
productivity.
In this embodiment mode, an amorphous semiconductor is used as a
semiconductor layer, and a semiconductor layer having one
conductivity may be formed as needed. In this embodiment mode, a
semiconductor layer and an n-type amorphous semiconductor layer as
a semiconductor layer having one conductivity are stacked. Further,
an NMOS structure of an n-channel thin film transistor in an n-type
semiconductor layer, a PMOS structure of a p-channel thin film
transistor in which a p-type semiconductor layer is formed, or a
CMOS structure of an n-channel thin film transistor and a p-channel
thin film transistor can be manufactured. In this embodiment mode,
the transistor 220 is an n-channel inversely staggered thin film
transistor. Furthermore, a channel protective-type inversely
staggered thin film transistor provided with a protective layer
over a channel region of the semiconductor layer can be used.
In addition, in order to impart conductivity, an n-channel thin
film transistor and a p-channel thin film transistor can also be
formed by adding an element imparting conductivity by doping and
forming an impurity region in the semiconductor layer. Instead of
forming the n-type semiconductor layer, conductivity may be
imparted to the semiconductor layer by performing plasma treatment
with a PH.sub.3 gas.
A semiconductor can be formed using an organic semiconductor
material by a printing method, a spray method, a spin coating
method, a droplet discharging method, a dispenser method, or the
like. In this case, since the above etching step is not necessary,
the number of steps can be reduced. As an organic semiconductor, a
low molecular organic material, a high molecular organic material,
an organic coloring matter, a conductive high molecular organic
material, or the like can be employed. A .pi.-conjugated high
molecular material with the skeleton including conjugated double
bonds is desirably used as an organic semiconductor material in the
present invention. Typically, a soluble high molecular material
such as polythiophene, polyfluorene, poly(3-alkyl thiophene), a
polythiophene derivative, or pentacene can be used.
Next, a structure of a backlight unit 352 is explained. The
backlight unit 352 includes a cold cathode tube, a hot cathode
tube, a light emitting diode, an inorganic EL, or an organic EL as
a light source 331 that emits light, a lamp reflector 332 to
effectively lead light to a light conducting plate 335, the light
conducting plate 335 by which light is totally reflected and light
is led to the entire surface of the display panel, a diffusing
plate 336 for reducing variations in brightness, and a reflector
plate 334 for reusing light leaked under the light conducting plate
335.
A control circuit for controlling the luminance of the light source
331 is connected to the backlight unit 352. The luminance of the
light source 331 can be controlled by a signal supplied from the
control circuit.
A stacked layer of the third layer 233 including a polarizer and
the fourth layer 234 including a polarizer are provided between the
substrate 200 and the backlight unit 352. A stacked layer of the
first layer 231 including a polarizer and the second layer 232
including a polarizer are stacked on the opposite substrate 210.
The third layer 233 including a polarizer and the fourth layer 234
including a polarizer, which are provided on the backlight side,
are arranged to be in a parallel Nicols state. The first layer 231
including a polarizer and the second layer 232 including a
polarizer, which are provided on the viewing side, are arranged so
as to deviate from a parallel Nicols state. In such a structure,
one of a pair of the stacked layers each including a polarizer,
preferably the stacked polarizers on the viewing side are deviated,
which is a feature of the present invention. Accordingly, the
contrast ratio can be enhanced. In this embodiment mode, wavelength
distributions of extinction coefficients with respect to absorption
axes of the first layer 231 including a polarizer and the second
layer 232 including a polarizer are different from each other.
Similarly, wavelength distributions of extinction coefficients with
respect to absorption axes of the third layer 233 including a
polarizer and the fourth layer 234 including a polarizer are
different from each other.
The stacked layer of the third layer 233 including a polarizer and
the fourth layer 234 including a polarizer and the stacked layer of
the first layer 231 including a polarizer and the second layer 232
including a polarizer are bonded to the substrate 200 and the
opposite substrate 210, respectively. Further, a retardation film
may be stacked to be interposed between the stacked layer including
a polarizer and the substrate.
The stacked polarizers having different wavelength distributions of
extinction coefficients are provided and arranged so that the
absorption axes thereof are deviated in such a liquid crystal
display device, thereby the contrast ratio can be enhanced. In the
present invention, a plurality of polarizers can be made a layer
including polarizer having a staked-layer structure, which is
different from a structure in which a thickness of a polarizer is
simply made thick. The stacked polarizer deviates, thereby the
contrast ratio can be enhanced as compared with that of the
structure in which a thickness is simply made thick.
This embodiment mode can be freely combined with the above
embodiment modes.
Embodiment Mode 8
In this embodiment mode, operation of each circuit or the like
included in a display device will be explained.
FIG. 24A shows a system block view of a pixel portion 505 and a
driver circuit portion 508 of a display device.
In the pixel portion 505, a plurality of pixels is included, and a
switching element is provided in each intersection region of a
signal line 512 and a scanning line 510 that becomes a pixel. By
the switching elements, application of a voltage to control tilt of
liquid crystal molecules can be controlled. Such a structure where
switching elements are provided in each intersecting region is
referred to as an active type. The pixel portion of the present
invention is not limited to such an active type, and may have a
passive type structure instead. The passive type can be formed by a
simple process because each pixel does not have a switching
element.
The driver circuit portion 508 includes a control circuit 502, a
signal line driver circuit 503, and a scanning line driver circuit
504. The control circuit 502 has a function to control a gray scale
in accordance with display contents of the pixel portion 505.
Therefore, the control circuit 502 inputs a signal generated to the
signal line driver circuit 503 and the scanning line driver circuit
504. When a switching element is selected through a scanning line
510 in accordance with the scanning line driver circuit 504, a
voltage is applied to a pixel electrode in a selected intersecting
region. The value of this voltage is determined based on a signal
inputted from the signal line driver circuit 503 through the signal
line.
Further, in the control circuit 502, a signal controlling electric
power supplied to a lighting unit 506 is generated, and the signal
is inputted to a power supply 507 of the lighting unit 506. The
backlight unit shown in the above embodiment mode can be used for
the lighting unit. It is to be noted that the lighting unit
includes a front light besides a backlight. A front light is a
platy light unit formed of an illuminant and a light conducting
body, which is attached to a front side of a pixel portion and
illuminates the whole place. By such a lighting unit, the pixel
portion can be evenly illuminated with low power consumption.
As shown in FIG. 24B, the scanning line driver circuit 504 includes
circuits serving as a shift register 541, a level shifter 542, and
a buffer 543. Signals such as a gate start pulse (GSP) and a gate
clock signal (GCK) are inputted to the shift register 541. It is to
be noted that the scanning line driver circuit of the present
invention is not limited to the structure shown in FIG. 24B.
Further, as shown in FIG. 24C, the signal line driver circuit 503
includes circuits serving as a shift register 531, a first latch
532, a second latch 533, a level shifter 534, and a buffer 535. The
circuit serving as the buffer 535 is a circuit having a function
for amplifying a weak signal and includes an operational amplifier
and the like. Signals such as start pulses (SSP) are inputted to
the level shifter 534, and data (DATA) such as video signals is
inputted to the first latch 532. Latch (LAT) signals can be
temporarily held in the second latch 533, and are inputted to the
pixel portion 505 concurrently. This operation is referred to as a
line sequential drive. Therefore, a pixel that performs not a line
sequential drive but a dot sequential drive does not require the
second latch. Thus, the signal line driver circuit of the present
invention is not limited to the structure shown in FIG. 24C.
The signal line driver circuit 503, the scanning line driver
circuit 504, and the pixel portion 505 as described above can be
formed of semiconductor elements provided over one substrate. The
semiconductor element can be formed using a thin film transistor
provided over a glass substrate. In this case, a crystalline
semiconductor film may be applied to the semiconductor element
(refer to Embodiment Mode 5). A crystalline semiconductor film can
constitute a circuit included in a driver circuit portion because
it has a high electrical characteristic, in particular, mobility.
Further, the signal line driver circuit 503 and the scanning line
driver circuit 504 may be mounted on a substrate by using an IC
(Integrated Circuit) chip. In this case, an amorphous semiconductor
film can be applied to a semiconductor element in a pixel portion
(refer to Embodiment Mode 7).
In such a display device, stacked polarizers having different
wavelength distributions of extinction coefficients are provided
and arranged so that their absorption axes are deviated from each
other, thereby the contrast ratio can be enhanced. In other words,
the contrast ratio of light from a lighting unit controlled by a
control circuit can be enhanced.
Embodiment Mode 9
In this embodiment mode, a structure of a backlight will be
explained. A backlight is provided in a display device as a
backlight unit having a light source. The light source is
surrounded by a reflector plate so that the backlight unit
effectively scatters light.
As shown in FIG. 19A, a cold cathode tube 401 can be used as a
light source in a backlight unit 352. In order to reflect light
efficiently from the cold cathode tube 401, a lamp reflector 332
can be provided. The cold cathode tube 401 is mostly used for a
large-sized display device due to the intensity of the luminance
from the cold cathode tube. Therefore, the backlight unit having a
cold cathode tube can be used for display of a personal
computer.
As shown in FIG. 19B, a light emitting diode (LED) 402 can be used
as a light source in a backlight unit 352. For example, light
emitting diodes (W) 402 emitting a white color are each arranged at
predetermined intervals. In order to reflect light efficiently from
the light emitting diode (W) 402, a lamp reflector 332 can be
provided.
As shown in FIG. 19C, light emitting diodes (LED) 403, 404, and 405
each emitting a color of RGB can be used as a light source in a
backlight unit 352. When the light emitting diodes (LED) 403, 404,
and 405 emitting each color of RGB are used, a color reproduction
property can be enhanced as compared with a case when only the
light emitting diode (W) 402 emitting a white color is used. In
order to reflect light efficiently from the light emission diode
(W) 402, a lamp reflector 332 can be provided.
As shown in FIG. 19D, when light emitting diodes (LED) 403, 404,
and 405 each emitting a color of RGB is used as a light source, it
is not necessary that the number and arrangement thereof is the
same for all. For example, a plurality of light emitting diodes
emitting a color that has low light emitting intensity (such as
green) may be arranged.
The light emitting diode 402 emitting a white color and the light
emitting diodes (LED) 403, 404, and 405 each emitting color of RGB
may be combined.
When a field sequential method is applied in a case of using the
light emitting diodes of RGB, color display can be performed by
sequentially lighting the light emitting diodes of RGB in
accordance with the time.
The light emitting diode is suitable for a large-sized display
device because the luminance is high when the light emitting diode
is used. In addition, a color reproduction property of the light
emitting diode is superior to that of a cold cathode tube because
the color purity of each color of RGB is favorable, and an area
required for arrangement can be reduced. Therefore, a narrower
frame can be achieved when the light emitting diode is applied to a
small-sized display device.
Further, a light source needs not provided as a backlight unit
shown in FIGS. 19A to 19D. For example, when a backlight having a
light emitting diode is mounted on a large-sized display device,
the light emitting diode can be arranged on the back side of the
substrate. In this case, each of the light emitting diodes can be
sequentially arranged at predetermined intervals. A color
reproduction property can be enhanced in accordance with the
arrangement of the light emitting diodes.
Stacked layers each including a polarizer are arranged so that the
absorption axes of the polarizers are deviated from each other and
provided in a display device using such a backlight, thereby an
image having a high contrast ratio can be provided. A backlight
having a light emitting diode is particularly suitable for a
large-sized display device, and an image having high quality can be
provided even in a dark place by enhancing the contrast ratio of
the large-sized display device.
Embodiment Mode 10
Driving methods of a liquid crystal for a liquid crystal display
device include a vertical electric field method where a voltage is
applied perpendicularly to a substrate and a horizontal electric
field method where a voltage is applied parallel to a substrate.
The structure in which stacked layers each including polarizers are
arranged so that their absorption axes are deviated can be applied
to either the vertical electric field method or the horizontal
electric field method. In this embodiment mode, various kinds of
liquid crystal modes will be explained, to which stacked layers
each including polarizers that are arranged so that their
absorption axes are deviated from each other can be applied.
First, FIGS. 27(A1) and 27(A2) each show a schematic diagram of a
liquid crystal display device of a TN mode.
Similar to the above embodiment modes, a layer 100 including a
display element is interposed between a first substrate 101 and a
second substrate 102, which are arranged to be opposite to each
other. A first layer 103 including a polarizer and a second layer
102 including a polarizer are arranged so as to deviate from a
parallel Nicols state on the first substrate 101 side. A third
layer 105 including a polarizer and a fourth layer 106 including a
polarizer are arranged to be in a parallel Nicols state on the
second substrate 102 side. The first layer 103 including a
polarizer and the third layer 105 including a polarizer are
arranged to be in a crossed Nicols state.
Although not shown, a backlight or the like is arranged on an outer
side of the fourth layer 106 including a polarizer. A first
electrode 108 and a second electrode 109 are respectively provided
over the first substrate 101 and the second substrate 102. The
first electrode 108 on a side opposite to the backlight, in other
words, on the viewing side, is formed so as to have at least a
light transmitting property.
When a liquid crystal display device having such a structure is in
a normally white mode, when a voltage is applied to the first
electrode 108 and the second electrode 109 (referred to as a
vertical electric field method), black display is performed as
shown in FIG. 27(A1). At that time, liquid crystal molecules are
aligned vertically. Thus, light from the backlight cannot pass
through the substrate, which leads to black display.
As shown in FIG. 27(A2), when a voltage is not applied between the
first electrode 108 and the second electrode 109, white display is
performed. At that time, liquid crystal molecules are aligned
horizontally while twisted on a plane. As a result, light from the
backlight can pass through the substrate provided with a stacked
layer including a polarizer that is arranged on the viewing side so
as to deviate from a parallel Nicols state, which is a pair of the
stacked layers including a polarizer, thereby a predetermined image
is displayed.
By providing a color filter at that time, full-color display can be
performed. The color filter can be provided on either the first
substrate 101 side or the second substrate 102 side.
A known material may be used for a liquid crystal material of the
TN mode.
FIG. 27(B1) shows a schematic diagram of a liquid crystal display
device of a VA mode. A VA mode is a mode where liquid crystal
molecules are aligned perpendicularly to a substrate when there is
no electric field.
Similarly to FIGS. 27(A1) and 27(A2), a first electrode 108 and a
second electrode 109 are respectively provided over a first
substrate 101 and a second substrate 102. In addition, the first
electrode 108 on a side opposite to the backlight, in other words,
on the viewing side, is formed so as to have at least a light
transmitting property. A first layer 103 including a polarizer and
a second layer 104 including a polarizer are arranged so as to
deviate from a parallel Nicols state. Further, on the second
substrate 102 side, a third layer 105 including a polarizer and a
fourth layer 106 including a polarizer are arranged to be in a
parallel Nicols state. The first layer 103 including a polarizer
and the third layer 105 including a polarizer are arranged to be in
a crossed Nicols state.
When a voltage is applied to the first electrode 108 and the second
electrode 109 (vertical electric field method) in a liquid crystal
display device having such a structure, white display is performed,
which means an on state, as shown in FIG. 27(B1). At that time,
liquid crystal molecules are aligned horizontally. Thus, light from
the backlight can pass through the substrate provided with the
stacked layers each including a polarizer that are deviated from a
parallel Nicols state, thereby a predetermined image is displayed.
By providing a color filter at that time, full-color display can be
performed. The color filter can be provided on either the first
substrate 101 side or the second substrate 102 side.
As shown in FIG. 27(B2), when no voltage is applied between the
first electrode 108 and the second electrode 109, black display is
performed, which means an off state. At that time, liquid crystal
molecules are aligned vertically. Thus, light from the backlight
cannot pass through the substrate, which leads to black
display.
Thus, in an off state, liquid crystal molecules are perpendicular
to the substrate, thereby black display is performed. Meanwhile, in
an on state, liquid crystal molecules are parallel to the
substrate, thereby white display is performed. In an off state,
liquid crystal molecules rise; therefore, polarized light from the
backlight passes through a cell without being affected by the
liquid crystal molecules and can be completely blocked by the layer
including a polarizer on the opposite substrate side. Accordingly,
at least one of the layers including a stacked polarizer of a pair
of the layers including a stacked polarizer is arranged so as to
deviate from a parallel Nicols state, thereby further enhancement
of the contrast ratio can be assumed.
FIGS. 27(C1) and 27(C2) show an example in which a stacked layer
including a polarizer of the present invention is applied to an MVA
mode where alignment of liquid crystal is divided. The MVA mode is
a method in which one pixel is divided into a plurality and the
viewing angle dependency for each portion is compensated for that
of other portions. As shown in FIG. 27(C1), projections 158 and
159, the cross-section of each of which is a triangle shape, are
respectively provided on a first electrode 108 and a second
electrode 109. When a voltage is applied to the first electrode 108
and the second electrode 109 (vertical electric field method),
white display is performed, which means an on state, as shown in
FIG. 27(C1). At that time, liquid crystal molecules are aligned so
as to tilt toward the projections 158 and 159. Thus, light from the
backlight can pass through the substrate provided with the stacked
layers each including a polarizer that are deviated from a parallel
Nicols state, thereby predetermined image display can be performed.
By providing a color filter at that time, full-color display can be
performed. The color filter can be provided on either the first
substrate 101 side or the second substrate 102 side.
As shown in FIG. 27(C2), when a voltage is not applied between the
first electrode 108 and the second electrode 109, black display is
performed, which means an off state. At that time, liquid crystal
molecules are aligned vertically. Thus, light from the backlight
cannot pass through the substrate, which leads to black
display.
FIGS. 30A and 30B show a top view and a cross-sectional view of
another example of an MVA mode. In FIG. 30A, a second electrode is
formed into a bent pattern of a dog-legged shape to be second
electrodes 109a, 109b, and 109c. An insulating layer 162 that is an
orientation film is formed over the second electrodes 109a, 109b,
and 109c. As shown in FIG. 30B, a projection 158 is formed over a
first electrode 108 to have a shape corresponding to that of the
second electrodes 109a, 109b, and 109c. Openings of the second
electrodes 109a, 109b, and 109c serve as projections, which can
move the liquid crystal molecules.
FIGS. 28(A1) and 28(A2) each show a schematic diagram of a liquid
crystal display device of an OCB mode. In the OCB mode, alignment
of liquid crystal molecules forms a compensation state optically in
a liquid crystal layer, which is referred to as a bent
orientation.
Similarly to FIGS. 27(A1) to 27(C2), a first electrode 108 and a
second electrode 109 are respectively provided on a first substrate
101 and a second substrate 102. Although not shown, a backlight or
the like is arranged on an outer side of a fourth layer 106
including a polarizer. In addition, the first electrode 108 on a
side opposite to the backlight, in order words, on the viewing
side, is formed so as to have at least a light transmitting
property. A first layer 103 including a polarizer and a second
layer 104 including a polarizer are arranged so as to deviate from
a parallel Nicols state. A third layer 105 including a polarizer
and the fourth layer 106 including a polarizer are arranged on the
second substrate 102 side so as to be in a parallel Nicols state.
The first layer 103 including a polarizer and the third layer 105
including a polarizer are arranged so as to be in a crossed Nicols
state.
When a constant on-voltage is applied to the first electrode 108
and the second electrode 109 (vertical electric field method) in a
liquid crystal display device having such a structure, black
display is performed as shown in FIG. 28(A1). At that time, liquid
crystal molecules are aligned vertically. Thus, light from the
backlight cannot pass through the substrate, which leads to black
display.
When a constant off-voltage is applied between the first electrode
108 and the second electrode 109, white display is performed as
shown in FIG. 28(A2). At that time, liquid crystal molecules are
aligned in a bent orientation. Thus, light from the backlight can
pass through the substrate provided with the stacked layer
including a polarizer, thereby a predetermined image is displayed.
By providing a color filter at that time, full-color display can be
performed. The color filter can be provided on either the first
substrate 101 side or the second substrate 102 side.
In such an OCB mode, a stacked layer including a polarizer, which
is a pair of the stacked layers including a polarizer, on the
viewing side is arranged so as to deviate from a parallel Nicols
state, thereby birefringence caused in a liquid crystal layer can
be compensated. As a result, the contrast ratio and a wide viewing
angle can be enhanced.
FIGS. 28(B1) and (B2) each show a schematic diagram of an FLC mode
and an AFLC mode.
Similarly to FIGS. 27(A1) to 27(C2), a first electrode 108 and a
second electrode 109 are respectively provided on a first substrate
101 and a second substrate 102. The first electrode 108 on a side
opposite to a backlight, in other words, on a viewing side is
formed to have at least a light transmitting property. A first
layer 103 including a polarizer and a second layer 104 including a
polarizer are arranged so as to deviate from a parallel Nicols
state. A third layer 105 including a polarizer and a fourth layer
106 including a polarizer are arranged on the second substrate 102
side so as to be in a parallel Nicols state. The first layer 103
including a polarizer and the third layer 105 including a polarizer
are arranged so as to be in a crossed Nicols state.
When a voltage is applied to the first electrode 108 and the second
electrode 109 (referred to as vertical electric field method) in a
liquid crystal display device having such a structure, white
display is performed as shown in FIG. 28(B1). At that time, liquid
crystal molecules are aligned horizontally while rotated on a plane
surface. Thus, light from the backlight can pass through the
substrate provided with the stacked layer including a polarizer,
which is a pair of the stacked layers including a polarizer, on the
viewing side so as to deviate from a parallel Nicols state, thereby
a predetermined image is displayed.
When no voltage is applied between the first electrode 108 and the
second electrode 109, black display is performed as shown in FIG.
28(B2). At that time, liquid crystal molecules are aligned
horizontally. Thus, light from the backlight cannot pass through
the substrate, which leads to black display.
When a color filter is provided at that time, full-color display
can be performed. The color filter can be provided on either the
first substrate 101 side or the second substrate 102 side.
A known material may be used for a liquid crystal material of the
FLC mode and the AFLC mode.
FIGS. 29(A1) and 29(A2) each shows a schematic diagram of a liquid
crystal display device of an IPS mode. In the IPS mode, liquid
crystal molecules are constantly rotated in parallel to a
substrate, and a horizontal electric field method where electrodes
are provided on one substrate side is employed.
In the IPS mode, a liquid crystal is controlled by a pair of
electrodes provided on one substrate. Therefore, a pair of
electrodes 150 and 151 is provided over a second substrate 102. The
pair of electrodes 150 and 151 may each have a light transmitting
property. A first layer 103 including a polarizer and a second
layer 104 including a polarizer are arranged so as to deviate from
a parallel Nicols state. In addition, a third layer 105 including a
polarizer and a fourth layer 106 including a polarizer are arranged
on the second substrate 102 side so as to be in a parallel Nicols
state. The first layer 103 including a polarizer and the third
layer 105 including a polarizer are arranged so as to be in a
crossed Nicols state. Although not shown, a backlight or the like
is arranged on an outer side of the fourth layer 106 including a
polarizer.
When a voltage is applied to the pair of electrodes 150 and 151 in
a liquid crystal display device having such a structure, white
display is performed, which means an on state, as shown in FIG.
29(A1). Thus, light from the backlight can pass through the
substrate provided with the stacked layer including a polarizer,
which is one of a pair of the stacked layers including a polarizer,
on the viewing side, which deviates from a parallel Nicols state,
thereby a predetermined image is displayed.
By providing a color filter at that time, full-color display can be
performed. The color filter can be provided on either the first
substrate 101 side or on the second substrate 102 side.
When no voltage is applied between the pair of electrodes 150 and
151, black display is performed, which means an off state, as shown
in FIG. 29(A2). At that time, liquid crystal molecules are aligned
horizontally while rotated on a plane surface. Thus, light from the
backlight cannot pass through the substrate, which leads to black
display.
FIGS. 25A to 25D each show an example of the pair of electrodes 150
and 151 that can be used in the IPS mode. As shown in top views of
FIGS. 25A to 25D, the pair of electrodes 150 and 151 are
alternatively formed. In FIG. 25A, electrodes 150a and 151a have an
undulating wave shape. In FIG. 25B, electrodes 150b and 151b have a
concentric circular opening. In FIG. 25C, electrodes 150c and 151c
have a comb-like shape and are partially overlapped with each
other. In FIG. 25D, electrodes 150d and 151d have a comb-like shape
in which the electrodes are meshed with each other.
An FFS mode can be used instead of the IPS mode. The FFS mode has a
structure in which a pair of electrodes are not formed in the same
layer, and an electrode 153 is formed over an electrode 152 with an
insulating film interposed therebetween as shown in FIGS. 29(B1)
and 29(B2), while the pair of electrodes are formed on the same
surface in the IPS mode.
When a voltage is applied to the pair of electrodes 152 and 153 in
a liquid crystal display device having such a structure, white
display is performed, which means an on state, as shown in FIG.
29(B1). Thus, light from a backlight can pass through the substrate
provided with the stacked layer including a polarizer on the
viewing side that deviates from a parallel Nicols state, which is
one of a pair of layers including a stacked polarizer, thereby a
predetermined image is displayed.
By providing a color filter at that time, full-color display can be
performed. The color filter can be provided on either the first
substrate 101 side or on the second substrate 102 side.
When no voltage is applied between the pair of electrodes 152 and
153, black display is performed, which means an off state, as shown
in FIG. 29(B2). At that time, liquid crystal molecules are aligned
horizontally while rotated on a plane surface. Thus, light from the
backlight cannot pass through the substrate, which leads to black
display.
FIGS. 26A to 26D each show an example of the pair of electrodes 152
and 153 that can be used in the FFS mode. As shown in top views of
FIGS. 26A to 26D, the electrodes 153 that are formed into various
patterns are formed over the electrodes 152. In FIG. 26A, an
electrode 153a over an electrode 152a has a bent dog-legged shape.
In FIG. 26B, an electrode 153b over an electrode 152b has a
concentric circular shape. In FIG. 26C, an electrode 153c over an
electrode 152c has a comb-like shape in which the electrodes are
messed with other. In FIG. 26D, an electrode 153d over an electrode
152d has a comb-like shape.
A known material may be used for a liquid crystal material of the
IPS mode and the FFS mode.
A structure in which a stacked layer including a polarizer on the
viewing side, which is one of a pair of stacked layers including a
polarizer of the present invention, is arranged so as to deviate
from a parallel Nicols state is applied to a liquid crystal display
device of a vertical electric field method, thereby display with an
even higher contrast ratio can be performed. Such a vertical
electric field method is suitable for a display device for a
computer that is used in a room or for a large-sized
television.
Further, when the present invention is applied to a liquid crystal
display device of a horizontal electric field method, display with
a high contrast ratio can be performed in addition to one with a
viewing angle. Such a horizontal electric field method is suitable
for a portable display device.
Furthermore, the present invention can be applied to a liquid
crystal display device of a rotation mode, a scattering mode, or a
birefringence mode and a display device in which layers including a
polarizer are arranged on both sides of the substrate.
This embodiment mode can be freely combined with the above
embodiment modes.
Embodiment Mode 11
This embodiment mode will be explained with reference to FIGS. 18A
and 18B. FIGS. 18A and 18B show an example of forming a display
device (a liquid crystal display module) using a TFT substrate 2600
that is manufactured by applying the present invention.
FIG. 18A shows an example of a liquid crystal display module where
the TFT substrate 2600 and an opposite substrate 2601 are bonded
with a sealant 2602, and a pixel portion 2603 including a TFT or
the like and a liquid crystal layer 2604 are provided therebetween
so as to form a display region. A colored layer 2605 is necessary
for color display. For a case of an RGB method, colored layers
corresponding to each color of red, green, and blue are provided to
correspond to each pixel. A first layer 2606 including a polarizer
and a second layer 2626 including a polarizer are arranged on an
outer side of the opposite substrate 2601. A third layer 2607
including a polarizer, a fourth layer 2627 including a polarizer,
and a lens film 2613 are arranged on an outer side of the TFT
substrate 2600. A light source includes a cold cathode tube 2610
and a reflector plate 2611. A circuit board 2612 is connected to
the TFT substrate 2600 through a flexible wiring board 2609.
External circuits such as a control circuit and a power supply
circuit are included.
Stacked layers of the third layer 2607 including a polarizer and
the fourth layer 2627 including a polarizer which have different
wavelength distributions of extinction coefficients from each other
are provided between the TFT substrate 2600 and a backlight that is
the light source. The stacked layers of the first layer 2606
including a polarizer and the second layer 2626 including a
polarizer which have different wavelength distributions of
extinction coefficients from each other are provided over the
opposite substrate 2601. The third layer 2607 including a polarizer
and the fourth layer 2627 including a polarizer, which are provided
on the backlight side, are arranged so as to be in a parallel
Nicols state. The first layer 2606 including a polarizer and the
second layer 2626 including a polarizer, which are provided on the
viewing side, are arranged so as to be deviated from a parallel
Nicols state. In such a structure, one of a pair of the stacked
layers each including polarizers having different wavelength
distributions of extinction coefficients from each other,
preferably the stacked layers each including a polarizer on the
viewing side are deviated. Accordingly, the contrast ratio can be
enhanced.
The stacked layer of the third layer 2607 including a polarizer and
the fourth layer 2627 including a polarizer is bonded to the TFT
substrate 2600. The stacked layer of the first layer 2606 including
a polarizer and the second layer 2626 including a polarizer are
bonded to the opposite substrate 2601. In addition, a retardation
film may be stacked to be interposed between the stacked layer
including a polarizer and the substrate.
For the liquid crystal display module, a TN (Twisted Nematic) mode,
an IPS (In-Plane-Switching) mode, an FFS (Fringe Field Switching)
mode, an MVA (Multi-domain Vertical Alignment) mode, an ASM
(Axially Symmetric aligned Micro-cell) mode, an OCB (Optical
Compensated Birefringence) mode, an FLC (Ferroelectric Liquid
Crystal) mode, or the like can be used.
FIG. 18B shows an example of an FS-LCD (Field Sequential-LCD) in
which an OCB mode is applied to the liquid crystal display module
of FIG. 18A. The FS-LCD emits red light, green light, and blue
light during one frame period and can perform color display by
combining images using time division. Since each light is emitted
by a light emitting diode, a cold cathode tube, or the like, a
color filter is not necessary. Thus, it is not necessary to arrange
color filters of three primary colors and restrict the display
region of each color, and color display of all three colors can be
performed in any regions; therefore, nine times as many pixels can
be displayed in the same area. On the other hand, since three
colors of light are emitted during one frame period, high-speed
response is required for a liquid crystal. By employing an FS
method, an FLC mode, and an OCB mode to a display device of the
present invention, a display device or a liquid crystal television
device with high performance and high image quality can be
completed.
A liquid crystal layer in the OCB mode has a so-called .pi.-cell
structure. In the .pi.-cell structure, liquid crystal molecules are
oriented so that their pretilt angles are plane-symmetric along a
center plane between an active matrix substrate and an opposite
substrate. An orientation state of a in-cell structure becomes
splayed orientation when a voltage is not applied between the
substrates and shifts to bent orientation when a voltage is applied
therebetween. This bent orientation becomes a white display. When a
voltage is applied further, liquid crystal molecules of bent
orientation get oriented perpendicular to the both substrates so
that light is not transmitted. With the OCB mode, response with
about 10 times higher speed than a conventional TN mode can be
realized.
Moreover, as a mode corresponding to the FS method, an SS-FLC or an
HV-FLC using a ferroelectric liquid crystal (FLC) capable of
high-speed operation, or the like can also be used. The OCB mode
uses a nematic liquid crystal having relatively low viscosity,
while the HV-FLC or the SS-FLC uses a smectic liquid crystal. A
material of an FLC, a nematic liquid crystal, a smectic liquid
crystal, or the like can be used as the liquid crystal
material.
Moreover, optical response speed of a liquid crystal display module
gets higher by narrowing the cell gap of the liquid crystal display
module. In addition, the optical response speed can also get higher
by decreasing the viscosity of the liquid crystal material. The
increase in response speed is particularly advantageous when a
pixel in a pixel portion of a liquid crystal display module of a TN
mode or a dot pitch is less than or equal to 30 .mu.m.
FIG. 18B shows a transmissive liquid crystal display module, in
which a red light source 2910a, a green light source 2910b, and a
blue light source 2910c are provided as light sources. The light
sources are provided with a control portion 2912 in order to switch
the red light source 2910a, the green light source 2910b, and the
blue light source 2910c. The control portion 2912 controls light
emission of each color, so that light enters the liquid crystal to
combine images by time division, thereby performing color
display.
Thus, absorption axes of the polarizers included in the layers are
deviated from a parallel Nicols state, thereby light leakage in the
absorption axis direction can be reduced. Therefore, the contrast
ratio of the display device can be enhanced. A display device with
high performance and high image quality can be manufactured.
This embodiment mode can be used by being freely combined with the
above embodiment modes.
Embodiment Mode 12
This embodiment mode will be explained with reference to FIG. 23.
FIG. 23 shows an example of forming a display device using a
substrate 813 that is a TFT substrate manufactured by applying the
present invention.
FIG. 23 shows a display device portion 801 and a backlight unit
802. The display device portion 801 includes the substrate 813, a
pixel portion 814 including a TFT or the like, a liquid crystal
layer 815, an opposite substrate 816, a first layer 817 including a
polarizer, a second layer 818 including a polarizer, a third layer
811 including a polarizer, a fourth layer 812 including a
polarizer, a slit (lattice) 850, a driver circuit 819, and an FPC
837. The backlight unit 802 includes a light source 831, a lamp
reflector 832, a reflector plate 834, a light conducting plate 835,
and a light diffuser plate 836.
The display device of the present invention shown in FIG. 23 makes
it possible to perform three-dimensional display without any need
for special equipment such as glasses. The slit 850 with an opening
that is arranged on the backlight unit side transmits light that is
incident from the light source and made to be a striped shape.
Then, the light is incident on the display device portion 801. This
slit 850 can make parallax in both eyes of a viewer on the viewing
side. The viewer sees only a pixel for the right eye with the right
eye and only a pixel for a left eye with a left eye simultaneously.
Therefore, the viewer can see three-dimensional display. That is,
in the display device portion 801, light given a specific viewing
angle by the slit 850 passes through each pixel corresponding to an
image for the right eye and an image for the left eye, thereby the
image for the right eye and the image for the left eye are
separated into different viewing angles, and three-dimensional
display is performed.
The third layer 811 including a polarizer and the fourth layer 812
including a polarizer are provided and stacked between the
substrate 813 and the backlight that is the light source. The first
layer 817 including a polarizer and the second layer 818 including
a polarizer are provided and stacked over the opposite substrate
816. The third layer 811 including a polarizer and the fourth layer
812 including a polarizer which have different wavelength
distributions of extinction coefficients from each other, which are
provided on the backlight side, are arranged so as to be in a
parallel Nicols state. The first layer 817 including a polarizer
and the second layer 818 including a polarizer which have different
wavelength distributions of extinction coefficients from each
other, which are provided on the viewing side, are arranged so as
to deviate from a parallel Nicols state. In such a structure, one
of a pair of the layers including a stacked polarizer, preferably,
the stacked polarizer on the viewing side, has a polarizer that
deviates. Thus, even slight light leakage can be prevented and the
contrast ratio can be enhanced.
An electronic device such as a television device or a cellular
phone is manufactured with the use of a display device of the
present invention, thereby an electronic device with high
performance and high image quality, which can perform
three-dimension display, can be provided.
Embodiment Mode 13
By a display device formed by the present invention, a television
device (also, referred to as a television simply or a television
receiver) can be completed. FIG. 20 shows a block diagram of a main
structure of a television device. As for a display panel, any modes
of the following may be employed: as the structure shown in FIG.
16A, a case where only a pixel portion 701 is formed and a scanning
line driver circuit 703 and a signal line driver circuit 702 are
mounted by a TAB method as shown in FIG. 17B; a case where only the
pixel portion 701 is formed and the scanning line driver circuit
703 and the signal line driver circuit 702 are mounted by a COG
method as shown in FIG. 17A; a case where a TFT is formed as shown
in FIG. 16B, the pixel portion 701 and the scanning line driver
circuit 703 are formed over the same substrate, and the signal line
driver circuit 702 is independently mounted as a driver IC; a case
where the pixel portion 701, the signal line driver circuit 702,
and the scanning line driver circuit 703 are formed over the same
substrate as shown in FIG. 17C; and the like.
In addition, as another structure of an external circuit, a video
signal amplifier circuit 705 that amplifies a video signal among
signals received by a tuner 704, a video signal processing circuit
706 that converts the signals output from the video signal
amplifier circuit 705 into chrominance signals corresponding to
each colors of red, green, and blue, a control circuit 707 that
converts the video signal into an input specification of a driver
IC, or the like are provided on an input side of the video signal.
The control circuit 707 outputs signals to both a scanning line
side and a signal line side. In a case of digital driving, a signal
dividing circuit 708 may be provided on the signal line side and an
input digital signal may be divided into m pieces to be
supplied.
An audio signal among signals received by the tuner 704 is
transmitted to an audio signal amplifier circuit 709 and is
supplied to a speaker 713 through an audio signal processing
circuit 710. A control circuit 711 receives control information of
a receiving station (reception frequency) or sound volume from an
input portion 712 and transmits signals to the tuner 704 or the
audio signal processing circuit 710.
Such liquid crystal display modules are incorporated into each
chassis as shown in FIGS. 21A to 21C, thereby a television device
can be completed. When a liquid crystal display module shown in
FIGS. 18A and 18B are used, a liquid crystal television device can
be completed. When a display device having a three-dimension
display function as Embodiment Mode 11 is used, a television device
that can perform three-dimension display can be manufactured. A
main screen 2003 is formed by a display module, and a speaker
portion 2009, an operation switch, and the like are provided as
accessory equipment. In such a manner, a television device can be
completed by the present invention.
As shown in FIG. 21A, a display panel 2002 is incorporated in a
chassis 2001, and general TV broadcast can be received by a
receiver 2005. In addition, by connecting to a communication
network by wired or wireless connections via a modem 2004, one-way
(from a sender to a receiver) or two-way (between a sender and a
receiver or between receivers) information communication can be
carried out. The television device can be operated by using a
switch built in the chassis or a remote control unit 2006. A
display portion 2007 for displaying output information may also be
provided in the remote control unit 2006.
Further, the television device may include a sub-screen 2008 formed
using a second display panel to display channels, volume, or the
like, in addition to the main screen 2003. In this structure, the
main screen 2003 and the sub-screen 2008 can be formed using a
liquid crystal display panel of the present invention. The main
screen 2003 may be formed using an EL display panel having a
superior viewing angle, and the sub-screen 2008 may be formed using
a liquid crystal display panel capable of displaying sub-images
with lower power consumption. In order to reduce the power
consumption preferentially, the main screen 2003 may be formed
using a liquid crystal display panel, and the sub-screen 2008 may
be formed using an EL display panel such that the sub-screen can
flash on and off. By using the present invention, even when many
TFTs and electronic parts are used with such a large-sized
substrate, a highly reliable display device can be formed.
FIG. 21B shows a television device having a large display portion
with a size of, for example, 20 to 80 inches. The television device
includes a chassis 2010, a display portion 2011, a keyboard portion
2012 that is an operation portion, a speaker portion 2013, and the
like. The present invention is applied to the manufacturing of the
display portion 2011. The display portion of FIG. 21B uses a
substance capable of being bent, and therefore, the television
device has a bent display portion. Since the shape of the display
portion can be designed freely as described above, a television
device having the desired shape can be manufactured.
FIG. 21C shows a television device having a large display portion
with a size of, for example, 20 to 80 inches. The television device
includes a chassis 2030, a display portion 2031, a remote control
unit 2032 that is an operation portion, a speaker portion 2033, and
the like. The present invention is applied to the manufacturing of
the display portion 2031. The television device shown in FIG. 21C
is a wall-hanging type so does not require a large installation
space.
Birefringence of liquid crystal changes depending on a temperature.
Therefore, the polarization of light passing through the liquid
crystal changes, and a light leakage condition from a polarizer on
the viewing side changes. As a result, a change in the contrast
ratio is generated depending on the temperature of the liquid
crystal. It is desirable that a driving voltage be controlled so as
to keep the contrast ratio constant. In order to control the
driving voltage, an element for detecting the transmittance may be
arranged and the driving voltage may be controlled based on the
detection results. As the element for detecting the transmittance,
a photosensor including an IC chip can be used. In the display
device, an element for detecting the temperature may be arranged
and the driving voltage may be controlled based on the detection
results and the change in the contrast ratio with respect to the
temperature of the liquid crystal element. As the element for
detecting the temperature, a temperature sensor including an IC
chip can be used. In this case, the element for detecting the
transmittance and the element for detecting the temperature are
preferably arranged so as to be hidden in the chassis of the
display device.
For example, the element for detecting the temperature may be
arranged near a liquid crystal display element in a display device
of the present invention, which is mounted on the television
devices shown in FIGS. 21A to 21C, and then, information about the
change in temperature of the liquid crystal may be fed back to a
circuit for controlling the driving voltage. Since the element for
detecting the transmittance is preferably set in a position closer
to the viewing side, the element may be arranged on a surface of
the display screen to be covered with the chassis. Then,
information about the change in the transmittance that is detected
may be fed back to the circuit for controlling the driver voltage
in a way similar to the information about the temperature.
The present invention can adjust the contrast ratio minutely by
displacing absorption axes of stacked polarizers having different
wavelength distributions of extinction coefficients. Therefore, the
present invention can deal with a slight deviation of the contrast
ratio with respect to the temperature of the liquid crystal, and an
optimal contrast ratio can be made. Thus, polarizers are stacked so
that the polarizers having different wavelength distributions of
extinction coefficients are deviated from each other in advance so
that an optimal contrast ratio can be made depending on the
conditions (inside or outside of a room, climate, or the like)
where the display device of the present invention is used, thereby
a television device or an electronic device with high performance
and high image quality display can be provided.
As a matter of course, the present invention is not limited to the
television device. The present invention can be applied to various
applications such as a monitor of a personal computer, particularly
large-sized display media typified by an information display board
at train stations, airports, or the like, and an advertising
display board on the street.
Embodiment Mode 14
An electronic device of the present invention includes: a
television device (also simply referred to as a TV or a television
receiver), a camera such as a digital camera and a digital video
camera, a mobile phone set (also simply referred to as a cellular
phone set or a cellular phone), a portable information terminal
such as a PDA, a portable game machine, a monitor for a computer, a
computer, an audio reproducing device such as a car audio set, an
image reproducing device provided with a recording medium such as a
home-use game machine, and the like. Specific examples thereof will
be explained with reference to FIGS. 22A to 22E.
A portable information terminal shown in FIG. 22A includes a main
body 9201, a display portion 9202, and the like. The display device
of the present invention can be applied to the display portion
9202. Thus, a portable information terminal with a high contrast
ratio can be provided.
A digital video camera shown in FIG. 22B includes a display portion
9701, a display portion 9702, and the like. The display device of
the present invention can be applied to the display portion 9701.
Thus, a digital video camera with a high contrast ratio can be
provided.
A cellular phone set shown in FIG. 22C includes a main body 9101, a
display portion 9102, and the like. The display device of the
present invention can be applied to the display portion 9102. Thus,
a cellular phone set with a high contrast ratio can be
provided.
A portable television set shown in FIG. 22D includes a main body
9301, a display portion 9302, and the like. The display device of
the invention can be applied to the display portion 9302. Thus, a
portable television set with a high contrast ratio can be provided.
The display device of the present invention can be applied to
various types of television sets including a small-sized television
mounted on a portable terminal such as a cellular phone set, a
medium-sized television that is portable, and a large-sized
television (for example, 40 inches in size or more).
A portable computer shown in FIG. 22E includes a main body 9401, a
display portion 9402, and the like. The display device of the
present invention can be applied to the display portion 9402. Thus,
a portable computer with a high contrast ratio can be provided.
By the display device of the present invention, an electronic
device with a high contrast ratio can be provided.
Embodiment 1
In this embodiment, for a case of a transmission type liquid
crystal display device of a TN mode, the result of optical
calculation will be explained, in which polarizers each of which
has a different wavelength distribution of extinction coefficient
with respect to the absorption axis are stacked and the outermost
polarizer on the viewing side deviates from a crossed Nicols state
with respect to a polarizer on a backlight side. It is to be noted
that the contrast ratio indicates the ratio of transmittance in
white display (also referred to as white transmittance) to
transmittance in black display (also referred to as black
transmittance) (white transmittance/black transmittance).
Transmittance in white display and transmittance in black display
were each calculated, and then the contrast ratio was
calculated.
As for the calculation in this embodiment, a liquid crystal optical
calculation simulator LCD MASTER (made by Shintech Inc.) was used.
Optical calculations of transmittance were conducted using the LCD
MASTER. The optical calculations were conducted with a 2.times.2
matrix optical calculation algorithm where the wavelength range is
from 380 nm to 780 nm, in which multiple interference between
elements was not taken into account.
As shown in FIG. 31 and FIG. 32, optical arrangement of an optical
calculation object has a structure in which a polarizer 1, a
polarizer 2, a retardation film B2, a retardation film A2, a glass
substrate, liquid crystal, a glass substrate, a retardation film
A1, a retardation film B1, a polarizer 2, and a polarizer 1 are
sequentially stacked from a backlight. The polarizer 1 and the
polarizer 2 on the backlight side are polarizing plates having
different wavelength distributions of extinction coefficients and
each absorption axis thereof is at an angle of 135 degrees, so that
two polarizers are in a parallel Nicols state. The polarizer 2 and
the polarizer 1 on the viewing side are polarizing plates having
different wavelength distributions of extinction coefficients, and
the angle of the absorption axis of the polarizer 2 on the viewing
side is 45 degrees so that the polarizer 2 is in a crossed Nicols
state with the polarizer 1 on the backlight side. First, in order
to calculate the angle of an absorption axis of the polarizer 1 on
the viewing side at which the contrast ratio is the highest,
calculation of the contrast ratio was performed when the angle of
the absorption axis of the polarizer 1 on the viewing side was
turned by 30 degrees to 50 degrees. Here, when a voltage that was
applied to the liquid crystal was 0 V or 5 V, the contrast ratio
indicates the ratio of transmittance of 0 V (white) to
transmittance of 5 V (black) (transmittance at 0 V/transmittance at
5 V). It is to be noted that the calculation in this embodiment was
performed to obtain contrast ratio of light extracted to the
viewing side with respect to the luminance of the backlight.
Table 1 and Table 2 show property values of the polarizers 1 and 2
respectively. A thickness of each polarizer was 30 .mu.m. Table 3
shows birefringence values of the liquid crystal and Table 4 shows
other property values and orientation state of the liquid crystal
1. Table 5 shows physical property values and arrangement of the
retardation film A1 and the retardation film A2. Table 6 shows
physical property values and arrangement of the retardation film B1
and the retardation film B2. Each of the retardation films A1, A2,
B1, and B2 is a retardation film having a negative uniaxial
property.
TABLE-US-00001 TABLE 1 wavelength refraction index of refraction
index of extinction coefficient of extinction coefficient of (nm)
transmission axis absorption axis direction transmission axis
direction absorption axis direction 380 1.5 1.5 0.00565 0.0092 390
1.5 1.5 0.002 0.0095 400 1.5 1.5 0.001 0.0093 410 1.5 1.5 0.0006
0.0095 420 1.5 1.5 0.0004 0.01 430 1.5 1.5 0.0003 0.011 440 1.5 1.5
0.00029 0.0113 450 1.5 1.5 0.00026 0.0115 460 1.5 1.5 0.00024
0.0117 470 1.5 1.5 0.00022 0.0118 480 1.5 1.5 0.00021 0.012 490 1.5
1.5 0.0002 0.0119 500 1.5 1.5 0.000196 0.0123 510 1.5 1.5 0.0002
0.01225 520 1.5 1.5 0.0002 0.0123 530 1.5 1.5 0.0002 0.01225 540
1.5 1.5 0.0002 0.0123 550 1.5 1.5 0.0002 0.012 560 1.5 1.5 0.0002
0.0116 570 1.5 1.5 0.0002 0.0113 580 1.5 1.5 0.0002 0.0112 590 1.5
1.5 0.0002 0.0112 600 1.5 1.5 0.0002 0.012 610 1.5 1.5 0.0002
0.0115 620 1.5 1.5 0.0002 0.011 630 1.5 1.5 0.0002 0.0106 640 1.5
1.5 0.0002 0.0103 650 1.5 1.5 0.0002 0.0102 660 1.5 1.5 0.0002
0.0101 670 1.5 1.5 0.0002 0.01005 680 1.5 1.5 0.0002 0.01002 690
1.5 1.5 0.00018 0.01 700 1.5 1.5 0.00018 0.0099 710 1.5 1.5 0.00018
0.0091 720 1.5 1.5 0.00018 0.008 730 1.5 1.5 0.00018 0.0065 740 1.5
1.5 0.00018 0.0057 750 1.5 1.5 0.00016 0.005 760 1.5 1.5 0.00015
0.0042 770 1.5 1.5 0.00014 0.0035 780 1.5 1.5 0.00012 0.003
TABLE-US-00002 TABLE 2 wavelength refraction index of refraction
index of extinction coefficient of extinction coefficient of (nm)
transmission axis absorption axis direction transmission axis
direction absorption axis direction 380 1.5 1.5 0.00565 0.008 390
1.5 1.5 0.002 0.0082 400 1.5 1.5 0.001 0.0079 410 1.5 1.5 0.0006
0.0079 420 1.5 1.5 0.0004 0.0077 430 1.5 1.5 0.0003 0.0079 440 1.5
1.5 0.00029 0.008 450 1.5 1.5 0.00026 0.0085 460 1.5 1.5 0.00024
0.0086 470 1.5 1.5 0.00022 0.0087 480 1.5 1.5 0.00021 0.0096 490
1.5 1.5 0.0002 0.0095 500 1.5 1.5 0.000196 0.0095 510 1.5 1.5
0.0002 0.01 520 1.5 1.5 0.0002 0.0106 530 1.5 1.5 0.0002 0.011 540
1.5 1.5 0.0002 0.01105 550 1.5 1.5 0.0002 0.0115 560 1.5 1.5 0.0002
0.0126 570 1.5 1.5 0.0002 0.0136 580 1.5 1.5 0.0002 0.014 590 1.5
1.5 0.0002 0.0146 600 1.5 1.5 0.0002 0.0147 610 1.5 1.5 0.0002
0.0148 620 1.5 1.5 0.0002 0.0148 630 1.5 1.5 0.0002 0.0147 640 1.5
1.5 0.0002 0.0148 650 1.5 1.5 0.0002 0.0146 660 1.5 1.5 0.0002
0.0143 670 1.5 1.5 0.0002 0.014 680 1.5 1.5 0.0002 0.0135 690 1.5
1.5 0.00018 0.0125 700 1.5 1.5 0.00018 0.0124 710 1.5 1.5 0.00018
0.012 720 1.5 1.5 0.00018 0.011 730 1.5 1.5 0.00018 0.0105 740 1.5
1.5 0.00018 0.0102 750 1.5 1.5 0.00016 0.01 760 1.5 1.5 0.00015
0.0096 770 1.5 1.5 0.00014 0.0092 780 1.5 1.5 0.00012 0.009
TABLE-US-00003 TABLE 3 wavelength birefringence (nm) .DELTA.n 380
0.1095635 390 0.107924 400 0.1064565 410 0.105138 420 0.1039495 430
0.102876 440 0.1019025 450 0.1010175 460 0.100212 470 0.0994755 480
0.098801 490 0.0981815 500 0.0976125 510 0.0970875 520 0.0966025
530 0.0961545 540 0.095739 550 0.0953525 560 0.094994 570 0.094659
580 0.094347 590 0.094055 600 0.0937825 610 0.0935265 620 0.093286
630 0.0930605 640 0.0928485 650 0.092649 660 0.0924605 670 0.092282
680 0.092114 690 0.091955 700 0.0918045 710 0.091661 720 0.0915255
730 0.0913975 740 0.091275 750 0.0911585 760 0.0910475 770
0.0909425 780 0.0908415
TABLE-US-00004 TABLE 4 anisotropy of dielectric constant .DELTA.e
5.0 elastic constant K11 12 pN elastic constant K22 6 pN elastic
constant K33 17 pN rubbing direction of backlight side 315 degrees
direction rubbing direction of viewing side 45 degrees direction
pretilt angle of backlight side 5 degrees pretilt angle of viewing
side 5 degrees chiral reagent none thickness of cell 4 mm
TABLE-US-00005 TABLE 5 .DELTA.n.sub.xy .times. d 0 nm in all
wavelength region .DELTA.n.sub.xz .times. d 92.4 nm in all
wavelength region arrangement of retardation film A2 z axis with 45
degree of backlight side tilt towered direction opposite to pretilt
of liquid crystal on backlight side arrangement of retardation film
A1 z axis with 45 degree of viewing side tilt towered direction
opposite to pretilt of liquid crystal on viewing side
TABLE-US-00006 TABLE 6 .DELTA.n.sub.xy .times. d 0 nm in all
wavelength region .DELTA.n.sub.xz .times. d 73.92 nm in all
wavelength region arrangement of retardation film B2 z axis
direction arranged of backlight side vertically with respect to
grass substrate arrangement of retardation film B1 z axis direction
arranged of viewing side vertically with respect to grass
substrate
FIG. 33 shows results of the contrast ratio of the polarizer 1 on
the viewing side when turned with a wavelength of 550 nm.
From FIG. 33, it is found that, when the angle of the absorption
axis of the polarizer 1 on the viewing side is 40.6 degrees, the
highest contrast ratio is obtained and the angle of the absorption
axis deviates from the 45 degrees of a crossed Nicols state with
the polarizer on the backlight side by 4.4 degrees.
Next wavelength dependency of the contrast ratio was calculated.
Structure A of FIG. 34(a) is a structure in which the absorption
axis of the polarizer 1 on the viewing side in the structure of
FIG. 32 is arranged at an angle of 40.6 degrees. Structure B of
FIG. 34(b) is a structure in which the absorption axis of the
polarizer 1 on the viewing side in the structure A forms an angle
of 45 degrees with the polarizer on the backlight side in a crossed
Nicols state. Structure C of FIG. 34(c) is a structure in which
each polarizer used is the polarizer 1 and the outermost polarizer
1 on the viewing side is arranged at an angle of 40.6 degrees. FIG.
35 shows the wavelength distribution of the extinction coefficients
of the polarizer 1 and the polarizer 2. It is shown that the
extinction coefficient of the polarizer 1 is large in a shorter
wavelength range and the extinction coefficient of the polarizer 2
is small in a larger wavelength range. Note that the property
values of the polarizers 1 and 2; the property values of the liquid
crystal, the retardation plates A1, A2, B1, and B2; and arrangement
thereof are the same as in Table 1, Table 2, Table 3, Table 4,
Table 5, and Table 6.
The results of the contrast ratios of the 0 V transmittance and 5 V
transmittance on the viewing side in the structures A, B, and C are
shown in FIG. 36, and the magnified view in the case of the
wavelengths from 400 nm to 600 nm is shown in FIG. 37. When the
structure A and the structure B are compared, the structure A in
which the polarizing plates are stacked so as to deviate at a
wavelength other than a longer wavelength range of 690 nm or more
results in a higher contrast. Thus, it is found that the contrast
can be increased by stacking polarizing plates so that the
polarizing plates are deviated.
Further, when the structure A and the structure C are compared, in
which polarizing plates are deviated and stacked, the structure A
in which polarizers having different wavelength distributions of
extinction coefficients from each other with respect to the
absorption axes results in a higher contrast in a long wavelength
region. This increases the contrast ratio because the extinction
coefficient of the polarizer 1 is smaller than that of the
polarizer 2 in a long wavelength region, and the structure A in
which the polarizers 2 having a larger extinction coefficient in a
long wavelength region are stacked results in lower transmittance
when displaying black (5 V) in a long wavelength region as in FIG.
35.
From the above result, polarizers, each of which has different
wavelength distributions of extinction coefficients with respect to
the absorption axis, are stacked, and the polarizer on the viewing
side deviates from a crossed Nicols state with respect to the
polarizer on the backlight side, thereby the high contrast ratio
can be obtained.
This application is based on Japanese Patent Application serial No.
2006-023853 filed in Japan Patent Office on Jan. 31 in 2006, the
entire contents of which are hereby incorporated by reference.
* * * * *